Assessment MICRO Flashcards
Organisms that vary in size and shape are referred to as:
A. Psychrophilic
B. Thermophilic
C. Palisades
D. Pleomorphic
D. Pleomorphic
Cocci arranged in packets of eight are:
A. Tetrads
B. Cuboids
C. Palisades
D. Pleomorphic
B. Cuboids
A slimy colony on blood agar indicates that:
A. The blood agar is too old
B. The organism has a capsule
C. The plate was incubated too long
D. The plate was incubated at too high a temperature
B. The organism has a capsule
Capsules increase virulence by:
A. Preventing phagocytosis
B. Increasing phagocytosis
C. Blocking surface antibodies
D. Producing toxins
A. Preventing phagocytosis
The Quellung test depends on the antigenic specificity of the:
A. Nucleus
B. Cell wall
C. Flagella
D. Capsule
D. Capsule
Bacteria reproduce by:
A. Transverse binary fission
B. Longitudinal binary fission
C. Sporulation
D. Budding
A. Transverse binary fission
In Gram staining, the primary dye is:
A. mordant
B. Gram’s iodine
C. Crystal violet
D. The counterstain
C. Crystal violet
A mordant is used to:
A. Increase the affinity or binding of the dye
B. Serves as an acid dye in bacterial but not in fungal stains
C. Decolorize in the Gram stain
D. Counterstain in the Kinyoun stain
A. Increase the affinity or binding of the dye
The most critical part of the Gram stain is:
A. The counterstain, which if too long can make gram positive organisms look gram negative
B. The decolorizer, which if left on too long can make gram positive organisms look gram negative
C. The mordant, which if left too long can prevent decolorization
D. The crystal violet, which if too strong can make gram negative organisms look gram positive
B. The decolorizer, which if left on too long can make gram positive organisms look gram negative
In the Ziehl-Neelsen stain, the decolorizer is:
A. Heated saline
B. Acetone
C. Acetone-alcohol
D. Alcohol + HCl
D. Alcohol + HCl
Members of Enterobacteriaceae that are motile have what type of flagella?
A. Atrichous
B. Lophotrichous
C. Peritrichous
D. All of the above
C. Peritrichous
Tumbling motility is characteristic of:
A. Listeria
B. Propionobacterium acnes
C. Salmonella
D. Proteus
A. Listeria
Babes-Ernst granules are characteristic of:
A. Bacillus anthracis
B. Listeria monocytogenes
C. Mycobacterium tuberculosis
D. Corynebacterium diphtheriae
D. Corynebacterium diphtheriae
Peptococcus and Peptostreptococcus are both:
A. Anaerobic gram-positive cocci
B. Common agents of meningitis
C. Resistant to penicillin
D. Microaerophilic
A. Anaerobic gram-positive cocci
Propionobacteria are:
A. Anaerobic gram-positive rods
B. Anaerobic gram-negative rods
C. Aerobic gram-negative rods
D. Aerobic gram-positive rods
A. Anaerobic gram-positive rods
Bordet-Gengou agar contains:
A. Potato, glycerol, blood
B. Potato, glycerol, egg
C. PEA, blood
D. 7.5% NaCl, blood
A. Potato, glycerol, blood
The “satellite phenomenon” refers to:
A. Colonies of Brucella surrounding air bubbles in blood agar
B. Enhanced hemolysis of S. aureus colonies next to S. pyogenes colonies
C. Growth of Haemophilus next to colonies of S. aureus
D. Smaller colonies next to larger colonies of Listeria
C. Growth of Haemophilus next to colonies of S. aureus
Lactose fermentation usually differentiates:
A. Salmonella from E. coli
B. Salmonella from Shigella
C. E. coli from Enterobacter
D. N. meningitidis from N. gonorrhoeae
A. Salmonella from E. coli
A pH indicator is used in media for enterics to:
A. Enhance lactose fermentation
B. Detect carbohydrate fermentation
C. Detect the presence of amino acid split products
D. Inhibit growth of lactose negative contaminants
B. Detect carbohydrate fermentation
What is the purpose of crystal violet and bile salts in MacConkey agar?
A. Acts as a pH indicator
B. Inhibits swarming of bacteria
C. H2S indicator
D. Inhibits gram-positive bacteria
D. Inhibits gram-positive bacteria
TSI agar contains what proportion of dextrose: lactose: sucrose?
A. 1:10:10
B. 1:1:10
C. 10:10:1
D. 10:1:1
A. 1:10:10
Transgrow is a transport medium for:
A. Gonococci and Candida
B. Gonococci and meningococci
C. Gonococci and Haemophilus ducreyi
D. Meningococci and Haemophilus influenzae
B. Gonococci and meningococci
Phenylethyl alcohol is used in media to:
A. Inhibit gram-positive bacteria
B. Inhibit gram-negative bacteria
C. Stimulate gram-positive bacteria
D. Stimulate gram-negative bacteria
B. Inhibit gram-negative bacteria
A yellow butt and red slant in a TSI tube indicates fermentation of:
A. Lactose
B. Glucose
C. Lactose and glucose
D. Sucrose and lactose
B. Glucose
Bacteria are:
A. Unicellular, prokaryotic organisms
B. Multicellular, prokaryotic organisms
C. Unicellular, eukaryotic organisms
D. Multicellular, eukaryotic organisms
A. Unicellular, prokaryotic organisms
Bacteria are single-cell prokaryotic microorganisms.
Fungi and parasites are single-cell or multicellular eukaryotic organisms, as are plants and all higher animals.
Viruses are dependent on host cells for survival and therefore are not considered cellular organisms but rather infectious agents.
Dependent on host cells for survival and therefore are not considered cellular organisms but rather infectious agents:
A. Bacteria
B. Fungi
C. Parasites
D. Viruses
D. Viruses
Among clinically relevant organisms, bacteria are single-cell prokaryotic microorganisms. Fungi and parasites are single-cell or multicellular eukaryotic organisms, as are plants and all higher animals. Viruses are dependent on host cells for survival and therefore are not considered cellular organisms but rather infectious agents.
A group of teenagers became ill with nausea, vomiting, severe abdominal cramps, and diarrhea after eating undercooked hamburgers from a local restaurant. Two of the teenagers were hospitalized with hemolytic-uremic syndrome. Escherichia coli O157:H7 was isolated from the patient’s stools as well as from uncooked hamburgers. The H7 refers to which bacterial structure?
A. Peptidoglycan
B. Lipid A
C. Capsule
D. Flagella
D. Flagella
The flagellins of different bacterial species presumably differ from one another in primary structure. They are highly antigenic (H antigens), and some of the immune responses to infection are directed against these proteins.
The unique chemical structure of the cell wall of Mycobacterium spp. Is associated with the presence of:
A. N-glycolylmuramic acid and a decrease in lipid content
B. N-acetylmuramic acid and a decrease in lipid content
C. N-glycolylmuramic acid and an increase in lipid content
D. N-acetylmuramic acid and an increase in lipid content
C. N-glycolylmuramic acid and an increase in lipid content
Mycobacterium spp. have an unusual cell wall structure. The cell wall contains N-glycolylmuramic acid instead of N-acetylmuramic acid, and it has a very high lipid content, which creates a hydrophobic permeability barrier.
In the fall of 2001, a series of letters containing spores of Bacillus anthracis were mailed to members of the media and to U.S. Senate offices. The result was 22 cases of anthrax, with five deaths. The heat resistance of bacterial spores, such as those of Bacillus anthracis, is partly attributable to their dehydrated state and partly to the presence of large amounts of:
A. Diaminopimelic acid
B. D-Glutamic acid
C. Calcium dipicolinate
D. Sulfhydryl-containing proteins
C. Calcium dipicolinate
The heat resistance of spores is partly attributable to their dehydrated state and in part to the presence in the core of large amounts (5–15% of the spore dry weight) of calcium dipicolinate, which is formed from an intermediate of the lysine biosynthetic pathway.
Mycoplasma species lack which of the following components?
A. Both DNA and RNA
B. Lipids
C. Peptidoglycan
D. Ribosomes
C. Peptidoglycan
Microorganisms that lack cell walls (commonly called mycoplasmas and making up the class Mollicutes) and do not synthesize the precursors of peptidoglycan
Which feature distinguishes Erysipelothrix rhusiopathiae from other clinically significant non-spore-forming, gram-positive, facultatively anaerobic bacilli?
A. Tumbling motility
B. Beta-hemolysis
C. More pronounced motility at 25ºC than 37ºC
D. H2S production
D. H2S production
Erysipelothrix rhusiopathiae is the only gram-positive bacillus that produces hydrogen sulfide when inoculated into triple sugar iron agar.
In the bacterial growth cycle, growth ceases because nutrients are exhausted or toxic metabolic products have accumulated on the:
A. Exponential phase
B. Lag phase
C. Logarithmic phase
D. Stationary phase
D. Stationary phase
The use of 0.1% fuchsin substituted for safranin in the Gram-stain
procedure may enhance the visibility of the organisms:
A. Bordetella
B. Brucella
C. Legionella
D. Propionobacterium
C. Legionella
Because of their faint staining, Legionella spp. are not usually detectable directly in clinical material by Gram stain. The use of 0.1% fuchsin substituted for safranin in the Gram-stain procedure may enhance the visibility of the organisms.
Upon review of a sputum Gram stain, the technician notes that the nuclei of all of the neutrophils present in the smear are staining dark blue. The best explanation for this finding is:
A. The slide was inadequately decolorized with acetone/alcohol
B. The sputum smear was prepared too thin
C. The cellular components have stained as expected
D. The iodine was omitted from the staining procedure
A. The slide was inadequately decolorized with acetone/alcohol
Problems with analysis of Gram staining generally result from errors including interpretation of the slide (smear prepared too thick), excessive heat fixing, and improper decolorization. Inadequate decolorization with acetone alcohol results in a smear in which the host cells (neutrophils and squamous cells) as well as bacteria all appear blue
Before an AFB smear is reported as negative, it should be examined carefully by scanning at least _____ oil immersion fields
A. 10 oil immersion fields
B. 30 oil immersion fields
C. 100 oil immersion fields
D. 300 oil immersion fields
D. 300 oil immersion fields
Bailey and Scott’s: Before an AFB smear is reported as negative, it should be examined carefully by scanning at least 300 oil immersion fields (magnification ×1000), equivalent to three full horizontal sweeps of a smear that is 2 cm long and 1 cm wide. (DOH 2 cm x 3 cm)
The Schaeffer–Fulton stain can be used for demonstration of:
A. Capsule
B. Flagella
C. Metachromatic granules
D. Spores
D. Spores
The Schaeffer–Fulton stain is a technique designed to isolate endospores by staining any present endospores green, and any other bacterial bodies red.
The Leifson stain can be used for demonstration of:
A. Capsule
B. Flagella
C. Metachromatic granules
D. Spores
B. Flagella
The most common cause for failure of a GasPak anaerobic jar to establish an adequate environment for anaerobic incubation is:
A. The failure of the oxidation-reduction potential indicator system due to deterioration of methylene blue
B. The failure of the packet to generate adequate H2 and/or CO2
C. Condensation of water on the inner surface of the jar
D. Catalysts that have become inactivated after repeated use
D. Catalysts that have become inactivated after repeated use
The 2 most common causes of failure of GasPak system are a defective gasket in the jar lid that allows escape of gas from inside the jar and inactivated catalyst pellets.
Most blood agar plates are prepared with 5% or 10% red blood cells (RBCs) obtained from:
A. Rabbit
B. Sheep
C. Horse
D. Human
B. Sheep
Sheep RBCs are used in blood agar plates because they are readily available and less inhibitory than cells of other species. The type of hemolysis is determined by the source of RBCs. Sheep RBCs are chosen because of the characteristically clear hemolysis produced by β-hemolytic streptococci, Staphylococcus, and other pathogens producing β-hemolysins.
Sheep blood does not support the growth of Haemophilus haemolyticus, eliminating the possibility of confusing it with β-hemolytic streptococci in throat cultures.
Growth surrounded by yellow halos on mannitol salt agar indicates:
A. The organism cannot ferment mannitol
B. The organism cannot tolerate high salt concentrations
C. The organism can sustain high salt concentrations and ferment mannitol
D. None of the above
C. The organism can sustain high salt concentrations and ferment mannitol
Which of the following differentiates Thayer-Martin medium from Modified Thayer-Martin medium?
A. Nystatin
B. Vancomycin
C. Colistin
D. Trimethoprim lactate
D. Trimethoprim lactate
Which statement correctly describes the mode of action of the antibiotic listed for modified Thayer-Martin medium?
A. Colistin inhibits gram-positive bacteria
B. Nystatin inhibits fungi and molds
C. Vancomycin inhibits gram-negative bacteria
D. Trimethoprim lactate inhibits gram-positive bacteria
B. Nystatin inhibits fungi and molds
MTM: Modified Thayer-Martin Medium
1. Vancomycin inhibits the growth of gram-positive bacteria
2. Colistin inhibits the growth of gram-negative bacteria except N. gonorrhoeae
3. Nystatin inhibits the growth of fungi
4. Trimethoprim lactate prevents swarming of Proteus
All of the following are differential media except:
A. Blood agar
B. Chocolate agar
C. MacConkey’s agar
D. Eosin methylene blue agar
B. Chocolate agar
Select the medium best suited for the recovery of Yersinia enterocolitica from a patient with gastroenteritis:
A. Hektoen agar
B. Cefsulodin–Irgasan–Novobiocin (CIN) agar
C. Blood agar
D. Eosin-methylene blue agar
B. Cefsulodin–Irgasan–Novobiocin (CIN) agar
CIN agar inhibits the growth of many other organisms from the family Enterobacteriaceae. Yersinia spp. are also recovered from MacConkey and Salmonella-Shigella agars
Select the media of choice for recovery of Vibrio cholerae from a stool specimen;
A. MacConkey agar and thioglycollate media
B. Thiosulfate–citrate–bile–sucrose (TCBS) agar and alkaline peptone water (APW) broth
C. Blood agar and selenite-F (SEL) broth
D. CNA agar
B. Thiosulfate–citrate–bile–sucrose (TCBS) agar and alkaline peptone water (APW) broth
TCBS agar is used to grow Vibrio cholerae, which appear as yellow colonies as a result of the use of both citrate and sucrose. APW is used as an enrichment broth and should be subcultured to TCBS agar for further evaluation of Vibrio colonies
Which procedure is appropriate for culture of genital specimens in order to recover Chlamydia spp.?
A. Inoculate cycloheximide-treated McCoy cells
B. Plate onto blood and chocolate agar
C. Inoculate into thioglycollate (THIO) broth
D. Plate onto modified Thayer–Martin agar within 24 hours
A. Inoculate cycloheximide-treated McCoy cells
Chlamydiae are strict intracellular organisms and must be cultured using living cells
An organism was inoculated to a TSI tube and gave the following reactions: alkaline slant/acid butt, H2S, gas produced. This organism most likely is:
A. Klebsiella pneumoniae
B. Shigella dysenteriae
C. Salmonella typhimurium
D. Escherichia coli
C. Salmonella typhimurium
Salmonella is the only distractor that produces H2S. Also, Klebsiella and E. coli produce acid/acid reactions in TSI.
A patient presents with diarrhea and abdominal cramping. The organism isolated from the stool culture is identified as Shigella dysenteriae (group A). The TSI reaction would have indicated:
A. K/K
B. K/NC H2S+
C. A/A
D. K/A
D. K/A
The best medium for the isolation of Legionella is:
A. Iron cystine agar
B. Campy-this agar
C. V agar
D. Buffered charcoal yeast extract agar
D. Buffered charcoal yeast extract agar
The steam autoclave method of sterilization:
A. Uses 15 lbs of pressure for 15 minutes
B. Utilizes dry heat for 20 minutes
C. Produces a maximum temperature of 100ºC
D. Requires a source of ethylene oxide
A. Uses 15 lbs of pressure for 15 minutes
The traditional gravity displacement of steam sterilization cycle is 121˚C for 15 minutes at 15 pounds per square inch. Ethylene dioxide is an alternative sterilization method.
The biosafety level that includes most common laboratory microorganisms and involves organisms such as HBV, HIV and enteric pathogens is:
A. BSL-1
B. BSL-2
C. BSL-3
D. BSL-4
B. BSL-2
Seventy (70) % recirculated to the cabinet work area through HEPA; 30% balance can be exhausted through HEPA back into the room or to outside through a canopy unit:
A. BSC Class I
B. BSC Class II, A1
C. BSC Class II, A2
D. BSC Class II, B1
E. BSC Class II, B2
B. BSC Class II, A1
Thirty (30) % recirculated, 70% exhausted. Exhaust cabinet air must pass through a dedicated duct to the outside through a HEPA filter:
A. BSC Class I
B. BSC Class II, A1
C. BSC Class II, A2
D. BSC Class II, B1
E. BSC Class II, B2
D. BSC Class II, B1
The proper blood-to-broth ratio for blood cultures to reduce the antibacterial effect of serum in adults is:
A. 1:2
B. 1:3
C. 1:10
D. 1:30
C. 1:10
Human blood contains substance that may inhibit microbial growth. Diluting blood in culture broth reduces the concentration of these substances as well as any antibiotics that may be present. The recommended blood-broth ratio is 1:5 to 1:10. Dilutions less than this may cause blood to clot, trapping microorganisms in the clot. Greater dilutions may increase the time of detection.
SPS is used as an anticoagulant for blood cultures because it:
A. Inactivates penicillin and cephalosporins
B. Prevents clumping of red cells
C. Inactivates neutrophils and components of serum complement
D. Facilitates growth of anaerobes
C. Inactivates neutrophils and components of serum complement
Most commercially available blood culture media contain sodium polyanethol sulfonate (SPS) in concentration between 0.025 and 0.050%. SPS has anticoagulant activity and inactivates neutrophils as well as some antibiotics including gentamicin and polymyxin. It also precipitates components of serum complement.
Which of the following is the most appropriate method for collecting a urine specimen from a patient with an indwelling catheter?
A. Remove the catheter, cut the tip, and submit it for culture
B. Disconnect the catheter from the bag, and collect urine from the terminal end of the catheter
C. Collect urine directly from the bag
D. Aspirate urine aseptically from the catheter tubing
D. Aspirate urine aseptically from the catheter tubing
Indwelling catheters are closed systems, and should not be disconnected for specimen collection. Urine samples should not be collected from catheter bags, and Foley catheter tips are unsuitable for culture because they are contaminated with colonizing organisms. Urine from indwelling catheters should be collected by aseptically puncturing the tubing (collection port).
Which one of the following specimen requests is acceptable?
A. Feces submitted for anaerobic culture
B. Foley catheter tip submitted for aerobic culture
C. Rectal swab submitted for direct smear for gonococci
D. Urine for culture of acid-fast bacilli
D. Urine for culture of acid-fast bacilli
Urine is an appropriate specimen for the detection of renal tuberculosis. Since feces contain anaerobic organisms as part of the indigenous flora, it is an unacceptable specimen for anaerobic culture. Foley catheter tips are also not acceptable for culture because they are contaminated with colonizing organisms. Gram stain smears of rectal swabs for N. gonorrhoeae should also not be performed, since the presence of organisms with similar morphologies may lead to over interpretation of smears.
Transfer stool to ____ if transport will exceed 1 hour.
A. Amies
B. Cary-Blair
C. Eosin-methylene blue agar
D. Stuart’s
B. Cary-Blair
For patient preparation for wound swab, wipe the area with:
A. Amies medium
B. Stuart’s medium
C. Distilled water
D. Sterile saline or 70% alcohol
D. Sterile saline or 70% alcohol
Which of the following groups of specimens would be acceptable for anaerobic culture?
A. Vaginal, eye
B. Ear, leg tissue
C. Pleural fluid, brain abscess
D. Urine, sputum
C. Pleural fluid, brain abscess
Materials collected from sites not harboring indigenous normal flora (sterile body fluids, abscesses, exudates and tissue) should be culture for anaerobic bacteria, however, since anaerobes normally inhabit the skin and mucus membrane as part of indigenous normal flora, specimens such as urine, sputum and vaginal, eye and ear swabs are not acceptable for culture.
The optimal wound specimen for culture of anaerobic organisms should be:
A. A swab of lesion obtained before administration of antibiotics
B. A swab of lesion obtained after administration of antibiotics
C. A syringe filled with pus, obtained before administration of antibiotics
D. A syringe filled with pus, obtained after administration of antibiotics
C. A syringe filled with pus, obtained before administration of antibiotics
The use of swabs for collection of specimens for anaerobic culture is discouraged. Aspiration with a needle and syringe is recommended. Whenever possible cultures should be obtained before the administration of antibiotics to optimize organism recovery
CSF specimens must be transported in the laboratory:
A. In less than 15 mins
B. In less than 30 minutes
C. Within 1 hour
D. Within 2 hours
A. In less than 15 mins
Cerebrospinal fluid from a febrile 25-year-old man with possible meningitis is rushed to the laboratory for a stat Gram stain and culture. While performing the Gram stain, the technologist accidentally spills most of the specimen. The smear shows many neutrophils and no microorganisms. Since there is only enough CSF to inoculate one plate, the technologist should use a:
A. Blood agar plate
B. Chopped meat glucose
C. Chocolate agar plate
D. Thayer-Martin plate
C. Chocolate agar plate
Enriched media such as chocolate agar has no inhibitory effects on bacterial growth and contains additional nutrients that support the growth of fastidious organisms such as H. influenzae and Neisseria.
Serum for serologic studies may be frozen for up to 1 week at:
A. 4C
B. 37C
C. -20C
D. -70C
C. -20C
Urine, stool, viral specimens, sputa, swabs, and foreign devices such as catheters should be stored at 4°C. Serum for serologic studies may be frozen for up to 1 week at –20°C, and tissues or specimens for long-term storage should be frozen at –70°C.
In the Kirby-Bauer disc diffusion susceptibility test, which variable is critical when testing Pseudomonas species for antibiotic susceptibility to aminoglycosides?
A. Incubation temperature
B. Duration of incubation
C. Cation content of media
D. Depth of agar
C. Cation content of media
Variations in the concentrations of divalent cations, primarily calcium and magnesium affect the results of aminoglycoside, tetracycline and colistin test with Pseudomonas aeruginosa isolates. A cation concentration that is too high results in smaller zone sized and a concentration that is too low increase zone sizes.
Susceptibility testing performed on quality control organisms using a new media lot number yielded zone sizes that were too large for all antibiotics tested. The testing was repeated using media from a previously used lot number, and all zone sizes were acceptable. Which of the following best explains the unacceptable zone sizes?
A. The antibiotic disks were not stored with the proper desiccant
B. The depth of the media was too thick
C. The depth of the media was too thin
D. The antibiotic disks were not properly applied to the media
C. The depth of the media was too thin
All Mueller Hinton Agar used for disk diffusion susceptibility testing should be poured to a depth of 4mm. If the depth of the media is <4mm, this may be associated with excessively large zones and false positive susceptibility results. Agar that is >4mm in depth may cause excessively small zone sizes.
After satisfactory performance of daily disk diffusion susceptibility quality control is documented, the frequency of quality control can be reduced to:
A. Twice a week
B. Every week
C. Every other week
D. Every month
B. Every week
Daily disk diffusion quality control can be converted to weekly testing when 30 days of consecutive testing demonstrated no more than 3 antibiotic/ organism combinations outside the acceptable limits.
In disk diffusion susceptibility testing, as an antimicrobial agent diffuses away from the disk, the concentration of antibiotic is:
A. Increased
B. Decreased
C. Unchanged
D. Inoculum dependent
B. Decreased
The amount of antibiotic used in disk diffusion susceptibility testing is standardized and constant. Once the disk is placed on the inoculated plate and makes contact with the agar, the antibiotic in the disk begins to diffuse out. As it diffuses into the media, the concentration of antibiotic gets lower the further it diffuses from the disk.
In a disk diffusion susceptibility test, which of the following can result if disks are placed on the inoculated media and left at room temperature for an hour before incubation?
A. The antibiotic would not diffuse into the medium, resulting in no zone
B. Zones of smaller diameter would result
C. Zones of larger diameter would result
D. There would be no effect on the final zone diameter
C. Zones of larger diameter would result
A delay of more than 15 minutes between placing the disks on an inoculated plate and incubation permits excess prediffusion of the antimicrobial agent from the disk. This would result in a larger than expected zone diameter.
Which of the following factors would make an organism appear to be more resistant on a disk diffusion susceptibility test?
A. Too little agar in the plate
B. Too many organisms in the inoclum
C. Presence of 0.5% NaCl in the medium
D. A medium with pH of 7.4
B. Too many organisms in the inoclum
To ensure the reproducibility of disk diffusion testing, the inoculum must be standardized. If the inoculum is too dense (too many organisms) zone sizes would be smaller than expected and appear falsely resistant.
According to the Kirby–Bauer standard antimicrobial susceptibility testing method, what should be done when interpreting the zone size of a
motile, swarming organism such as a Proteus species?
A. The swarming area should be ignored
B. The results of the disk diffusion method are invalid
C. The swarming area should be measured as the growth boundary
D. The isolate should be retested after diluting to a McFarland standard
A. The swarming area should be ignored
A thin film of growth appearing in the zone area of inhibition around the susceptibility disk should be ignored when swarming Proteus or other organisms are encountered. Discontinuous, poor growth or tiny colonies near the end of the zone should also be ignored.
An antibiotic that inhibits cell wall synthesis is:
A. Chloramphenicol
B. Penicillin
C. Sulfamethoxazole
D. Colistin
B. Penicillin
Penicillin inhibits penicillin-binding proteins that are essential to peptidoglycan (cell wall) synthesis. Chloramphenicol inhibits protein synthesis, colistin increases cell membrane permeability and sulfamethoxazole inhibits folate metabolism.
Gram stain examination from a blood culture bottle shows dark blue, spherical organisms in clusters. Growth on sheep blood agar shows small, round, pale yellow colonies. Further tests should include:
A. Catalase production and coagulase test
B. Bacitracin susceptibility and serological typing
C. Oxidase and DNase reaction
D. Voges-Proskauer and methyl red test
A. Catalase production and coagulase test
The gram stain and culture growth describe a Staphylococcus species. Catalase production confi rms that the organism belong to the genus Staphylococcus and coagulase is used to differentiate S. aureus from coagulase negative staphylococci.
A Staphylococcus produced a fibrin clot in the tube coagulase test, but not in the slide coagulase test. This organism:
A. Produces only free coagulase and is most likely S. aureus
B. Produces only bound coagulase and is most likely S. aureus
C. Is most likely S. epidermidis because of the negative slide test
D. Is most likely S. epidermidis since the slide test is unreliable
A. Produces only free coagulase and is most likely S. aureus
Slide coagulase - cell-bound coagulase or clumping factor
Tube coagulase - free coagulase
A urine Gram stain shows gram-positive cocci in clusters. The organism tested catalase positive. To speciate this organism from culture, the
technician should perform a coagulase test and a/an:
A. Polymyxin B susceptibility
B. Novobiocin susceptibility
C. Oxidase
D. Beta-lactamase
B. Novobiocin susceptibility
The organism in this urine culture is a Staphylococcus species. Coagulase will differentiate S. aureus from coagulase negative staphylococci (CoNS) and novobiocin susceptibility will differentiate S. saprophyticus from other CoNS. S. saprophyticus is a common cause of urinary tract infections in young females
Which Staphylococcus species, in addition to S. aureus, also produces coagulase?
A. S. intermedius
B. S. saprophyticus
C. S. hominis
D. All of these options
A. S. intermedius
S. intermedius infects mammals and certain birds but not usually humans. Cases involving humans result from animal bites and are most often seen in persons who work closely with animals.
Which of the following tests should be used to differentiate
Staphylococcus aureus from Staphylococcus intermedius?
A. Acetoin
B. Catalase
C. Slide coagulase test
D. Urease
A. Acetoin
The production of acetoin by S. aureus from glucose or pyruvate differentiates it from S. intermedius, which is also coagulase positive.
This test is also called the VP test. Acetoin production is detected by addition of 40% KOH and 1% α-naphthol to the VP test broth after 48 hours of incubation. A distinct pink color within 10 minutes denotes a positive test.
Coagulase positive, PYR negative:
A. Staphylococcus epidermidis
B. Staphylococcus intermedius
C. Staphylococcus lugdunensis
D. Staphylococcus aureus
D. Staphylococcus aureus
Slime production is associated with which Staphylococcus species?
A. S. aureus
B. S. epidermidis
C. S. intermedius
D. S. saprophyticus
B. S. epidermidis
S. epidermidis produces an extracellular slime that enhances the adhesion of these organisms to indwelling plastic catheters. The slime production is considered a virulence factor and is associated with infections from prostheses.
Three sets of blood cultures were obtained from an adult patient with fever and suspected endocarditis. The aerobic bottle of one set had growth of Staphylococcus epidermidis at 5 days of incubation. This indicates that:
A. There was low-grade bacteremia
B. The organism is most likely a contaminant
C. The patient has a line infection
D. The blood culture bottles are defective
B. The organism is most likely a contaminant
Coagulase-negative staphylococci are commonly associated with contaminated blood cultures; however, they are also increasing as a cause of true bacteremia. Significant bacteremia in a patient with endocarditis is usually continuous and low grade. In most cases, all blood cultures drawn will yield positive results. The facts that only 1 bottle of 1 set was positive, and that the bottle did not become positive until day 5 of incubation indicate that this isolate is most likely a contaminant.
Which statement is incorrect for Staphylococcus epidermidis?
A. Coagulase negative
B. Fails to grow on mannitol salt agar
C. DNAse negative
D. Susceptible to novobiocin
B. Fails to grow on mannitol salt agar
Which of the following is not a member of family Micrococcaceae?
A. Staphylococcus
B. Streptococcus
C. Planococcus
D. Stomatococcus
B. Streptococcus
Inhibitor of Mannitol Salt Agar (MSA)
A. Mannitol
B. Phenol red
C. Neutral red
D. Sodium chloride
D. Sodium chloride
pH indicator of Mannitol Salt Agar (MSA)
A. Mannitol
B. Phenol red
C. Neutral red
D. Sodium chloride
B. Phenol red
Which test is used for the determination of inducible clindamycin resistance in staphylococci and streptococci?
A. E-test
B. D-zone test
C. A-test
D. CAMP test
B. D-zone test
By using a 15-μg erythromycin disk adjacent to a 2-μg clindamycin disk in a disk diffusionprocedure, a flattening of the clindamycin zone occurs in inducible clindamycin resistance, causing the zone to look like the letter D. This is referred to as being D-zone positive. CLSI recommends that inducible clindamycin resistant strains be reported as resistant with a comment that clindamycin may still be effective in some patients.
The D-zone susceptibility test is used to test inducible resistance on S. aureus strains demonstrating an initial antibiotic susceptibility profile of:
A. Erythromycin sensitive, clindamycin sensitive
B. Erythromycin resistant, clindamycin sensitive
C. Erythromycin resistant, clindamycin resistant
D. Erythromycin sensitive, clindamycin resistant
B. Erythromycin resistant, clindamycin sensitive
Green or brown color surrounding the colony:
A. Alpha hemolysis
B. Beta hemolysis
C. Gamma hemolysis
D. Alpha prime hemolysis
A. Alpha hemolysis
Not considered normal flora, presence in specimens is almost always considered clinically significant:
A. Streptococcus agalactiae
B. Streptococcus pyogenes
C. Enterococcus spp.
D. Viridans streptococci
B. Streptococcus pyogenes
Streptococcus pyogenes
Not considered normal flora
Inhabits skin and upper respiratory tract of humans, carried on nasal, pharyngeal, and, sometimes, anal mucosa; presence in specimens is almost always considered clinically significant
Streptolysin O:
A. Oxygen stable
B. Antigenic
C. Observed as surface hemolysis
D. All of these
B. Antigenic
Gram-positive cocci in chains are seen on a Gram stain from a blood culture. The organism grows as a beta-hemolytic colony. Further tests that could be performed include:
A. Bile esculin, PYR, bacitracin, and hippurate
B. Catalase and coagulase
C. Oxidase and DNase
D. VP and methyl red
A. Bile esculin, PYR, bacitracin, and hippurate
Bile esculin, PYR, bacitracin and hippurate are biochemical test for the presumptive or definitive identifi cation of beta hemolytic streptococci. Such as S. pyogenes, S. aggalactiae and Enterococcus.
A vaginal/rectal swab is collected from a pregnant patient to screen for group B Streptococcus colonization. What is the best medium to use for specimen inoculation?
A. Blood agar
B. LIM broth (Todd-Hewitt broth with colistin and nalidixic acid)
C. CNA agar
D. Thioglycollate broth
B. LIM broth (Todd-Hewitt broth with colistin and nalidixic acid)
Detection of group B streptococcus (GBS) in the genital and gastrointestinal tracts of pregnant women can identify infants at risk for GBS infection. The CDC recommends the collection of vaginal and rectal swab or a single swab inserted first into the vagina and then the rectum at 35 to 37 weeks of gestation. The swab(s) should be inoculated into a selective broth medium such as LIM broth (Todd-Hewitt broth with colistin and nalidixic acid). The use of vaginal/rectal swabs and selective broth medium greatly increases the recovery of GBS.
Which of the following organisms is able to hydrolyze hippurate and is positive in the CAMP test?
A. Streptococcus pyogenes
B. Streptococcus agalactiae
C. Streptococcus pneumoniae
D. Enterococcus faecalis
B. Streptococcus agalactiae
Viridans streptococci can be differentiated from Streptococcus pneumoniae by:
A. Alpha hemolysis
B. Morphology
C. Catalase
D. Bile solubility
D. Bile solubility
Bile solubility testing of alpha hemolytic streptococci differentiates S. pneumoniae (soluble) from other alpha-hemolytic streptococci such as viridans streptococci (insoluble).
The optochin (ethylhydrocupreine hydrochloride) disk is used for the identification of:
A. Haemophilus influenzae
B. Group A streptococci
C. Streptococcus pneumoniae
D. Alpha-hemolytic streptococci
C. Streptococcus pneumoniae
Optochin susceptibility is used to differentiate S. pneumoniae, which are susceptible from other alpha hemolytic streptococci which are resistant.
To be considered positive or sensitive to optochin, a zone of inhibition in diameter should be obtained with a 6-mm disk.
A. ≥ 6 mm
B. ≥ 10 mm
C. ≥ 14 mm
D. ≥ 16 mm
C. ≥ 14 mm
Which 2 diseases are usually preceded by infection with beta-hemolytic streptococci?
A. Rheumatic fever, undulant fever
B. Glomerulonephritis, rheumatic fever
C. Rheumatic fever, tularemia
D. Glomerulonephritis, undulant fever
B. Glomerulonephritis, rheumatic fever
Non-infectious sequelae associated with infection with Streptococcus pyogenes are glomerulonephritis and rheumatic fever.
Which reaction is incorrect for Enterococcus?
A. Positive growth in 6.5% salt broth
B. Positive hydrolysis of bile-esculin media
C. Negative catalase reaction
D. PYR negative
D. PYR negative
Colonies tend to dip down in the center and resemble a doughnut
(umbilicated) as they age; if organism has a polysaccharide capsule, colony may be mucoid; alpha-hemolytic:
A. Enterococcus faecalis
B. Leuconostoc sp.
C. Streptococcus pyogenes
D. Streptococcus pneumoniae
D. Streptococcus pneumoniae
Necrotizing fasciitis is a serious infection associated with:
A. Streptococcus agalactiae
B. Streptococcus mitis
C. Streptococcus pyogenes
D. Staphylococcus epidermidis
C. Streptococcus pyogenes
When streaking a throat culture on 5% sheep blood agar, stabbing the agar plate provides enhanced detection for:
A. Bile esculin hydrolysis
B. DNase activity
C. Streptolysin O
D. Streptolysin S
C. Streptolysin O
Streptolysin O - subsurface hemolysis
Streptolysin S - surface hemolysis
The bile solubility test causes the lysis of:
A. Streptococcus bovis colonies on a blood agar plate
B. Streptococcus pneumoniae colonies on a blood agar plate
C. Group A streptococci in broth culture
D. Group B streptococci in broth culture
B. Streptococcus pneumoniae colonies on a blood agar plate
The bile solubility test can be performed directly by dropping 2% sodium deoxycholate onto a few well-isolated colonies of S. pneumoniae. The bile salts speed up the autolysis observed in pneumococcal cultures. The colonies lyse and disappear when incubated at 35°C for 30 min, leaving a partially hemolyzed area on the plate.
In addition to Enterococcus faecalis, which other streptococci will grow in 6.5% salt broth?
A. Group A streptococci
B. Group B streptococci
C. Streptococcus pneumoniae
D. Group D streptococci (nonenterococci)
B. Group B streptococci
Approximately 80% of group B streptococci are capable of growing in 6.5% salt broth; however, they do not hydrolyze esculin or grow in media containing 4% bile salts.
The L-pyrrolidonyl-β-napthylamide (PYR)hydrolysis test is a presumptive test for which streptococci?
A. Group A and D (enterococcus) streptococci
B. Group A and B β-hemolytic streptococci
C. Nongroup A or B β-hemolytic streptococci
D. Streptococcus pneumoniae and group D nonenterococcus
A. Group A and D (enterococcus) streptococci
The PYR hydrolysis test is highly specifi c for group A streptococci and group D enterococci. The test detects the pyrrolidonylarylamidase enzyme, which hydrolyzes PYR.
A single ASO titer is considered to be moderately elevated if the titer is at least ____ Todd units in an adult.
A. 200 Todd units
B. 240 Todd units
C. 320 Todd units
D. 340 Todd units
B. 240 Todd units
A single ASO titer is considered to be moderately elevated if the titer is at least ____ Todd units in a child.
A. 200 Todd units
B. 240 Todd units
C. 320 Todd units
D. 340 Todd units
C. 320 Todd units
All of the following are appropriate when attempting to isolate N. gonorrhoeae from a genital specimen except:
A. Transport the genital swab in charcoal transport medium
B. Plate the specimen on modified Thayer–Martin (MTM) medium
C. Plate the specimen on New York City or Martin-Lewis agar
D. Culture specimens in ambient oxygen at 37°C
D. Culture specimens in ambient oxygen at 37°C
MTM, New York City, and Martin–Lewis agars contain blood factors needed to support the growth of N. gonorrhoeae as well as antibiotics that prevent growth of normal genital flora. Cultures must be incubated in 3%–7% CO2 at 35°C. Cultures should be held a minimum of 48 hours before being considered negative.
Semisolid transport media such as Amies, Stuart, or Cary–Blair are suitable for the transport of swabs for culture of most pathogens except:
A. Neisseria gonorrhoeae
B. Enterobacteriaceae
C. Campylobacter fetus
D. Streptococcus pneumoniae
A. Neisseria gonorrhoeae
Specimens for culture of N. gonorrhoeae are best if plated immediately or transported in a medium containing activated charcoal to absorb inhibitory substances that hinder their recovery.
The Superoxol test is used as a rapid presumptive test for:
A. Neisseria gonorrhoeae
B. Neisseria meningitidis
C. Neisseria lactamica
D. Moraxella (Branhamella) catarrhalis
A. Neisseria gonorrhoeae
Colonies are gray, translucent, smooth, glistening; may have dry, claylike consistency:
A. Neisseria animaloris
B. Neisseria elongata
C. Moraxella lacunata
D. Moraxella catarrhalis
B. Neisseria elongata
Large, nonpigmented or gray, opaque, smooth; friable “hockey puck” consistency; colony may be moved intact over surface of agar:
A. Neisseria gonorrhoeae
B. Neisseria elongata
C. Moraxella osloensis
D. Moraxella catarrhalis
D. Moraxella catarrhalis
A penicillin-resistant Neisseria gonorrhoeae produces:
A. Alpha-hemolysin
B. Beta-lactamase
C. Enterotoxin
D. Coagulase
B. Beta-lactamase
Antimicrobial resistance in Neisseria gonorrhea is widespread. The production of betalactamase (penicillinase) breaks open the beta lactam ring of penicillin, destroying its activity. Thus, N. gonorrhoeae that produces beta lactamase are resistant to penicillin.
A gram-negative diplococcus that grows on modified Thayer-Martin medium can be further confirmed as Neisseria gonorrhoeae if it is:
A. Oxidase positive, glucose positive, and maltose positive
B. Oxidase positive and glucose positive, maltose negative
C. Oxidase positive and maltose positive, glucose negative
D. Glucose positive, oxidase negative and maltose negative
B. Oxidase positive and glucose positive, maltose negative
Neisseria gonorrhoeae is oxidase positive and ferments glucose but not maltose
Xylose lysine deoxycholate (XLD) agar is a highly selective medium used for the recovery of which bacteria?
A. Staphylococcus spp. from normal flora
B. Yersinia spp. that do not grow on Hektoen agar
C. Enterobacteriaceae from gastrointestinal specimens
D. Streptococcus spp. from stool cultures
C. Enterobacteriaceae from gastrointestinal specimens
XLD agar is selective for gram-negative coliforms because of a high concentration (0.25%) of deoxycholate, which inhibits gram-positive bacteria.
In addition, XLD is differential for Shigella and Salmonella spp. The medium contains xylose, lactose, and sucrose, which are fermented by most normal intestinal coliforms producing yellow colonies.
Shigella does not ferment the sugars and produces red (or clear) colonies. Salmonella spp. ferment xylose; however, they also decarboxylate lysine in the medium, causing production of ammonia. Therefore, Salmonella first appear yellow but become red. Some Salmonella produce hydrogen sulfi de (H2S) from sodium thiosulfate and therefore appear as red colonies with black centers.
SITUATION: A group of elementary students became ill after eating undercooked ground beef prepared in the school cafeteria. The
suspected pathogen, E. coli serotype 0157:H7, is usually recovered using which of the following media?
A. XLD agar
B. MacConkey agar
C. MacConkey agar with sorbitol
D. Hektoen enteric agar
C. MacConkey agar with sorbitol
E. coli 0157:H7 ferments lactose, and therefore, appears as dark pink colonies on MacConkey agar. To differentiate E. coli 0157:H7 from normal fecal flora, MacConkey agar with sorbitol is used. E. coli 0157:H7 does not ferment sorbitol, and usually are colorless colonies.
Biochemically, the Enterobacteriaceae are gram-negative rods that:
A. Ferment glucose, reduce nitrate to nitrite, and are oxidase negative
B. Ferment glucose, produce indophenol oxidase, and form gas
C. Ferment lactose and reduce nitrite to nitrogen gas
D. Ferment lactose and produce indophenol oxidase
A. Ferment glucose, reduce nitrate to nitrite, and are oxidase negative
All Enterobacteriaceae ferment glucose and are oxidase negative and nonsporulating. Most Enterobacteriaceae are motile, but the genera Shigella and Klebsiella are not.
The Voges–Proskauer (VP) test detects which end product of glucose fermentation?
A. Acetoin
B. Nitrite
C. Acetic acid
D. Hydrogen sulfide
A. Acetoin
Acetoin or acetylcarbinol, an end product of glucose fermentation, is converted to diacetyl after the addition of the VP reagents (α-naphthol and 40% potassium hydroxide [KOH]). Diacetyl is seen as a red- to pink-colored complex
At which pH does the methyl red (MR) test become positive?
A. 7.0
B. 6.5
C. 6.0
D. 4.5
D. 4.5
Both MR and VP tests detect acid production from the fermentation of glucose. However, a positive MR test denotes a more complete catabolism of glucose to highly acidic end products such as formate and acetate than occurs with organisms that are VP positive only (e.g., Klebsiella pneumoniae).
A positive Simmons citrate test is seen as a:
A. Blue color in the medium after 24 hours of incubation at 35°C
B. Red color in the medium after 18 hours of incubation at 35°C
C. Yellow color in the medium after 24 hours of incubation at 35°C
D. Green color in the medium after 18 hours of incubation at 35°C
A. Blue color in the medium after 24 hours of incubation at 35°C
The Simmons citrate test determines if an organism can utilize citrate as the sole source of carbon. The medium turns blue, indicating the presence of alkaline products such as carbonate. Tubes are incubated a minimum of 24 hours at 35°C with a loose cap before reading.
Which of the following reagents is added to detect the production of indole?
A. p Dimethylaminobenzaldehyde
B. Bromcresol purple
C. Methyl red
D. Cytochrome oxidase
A. p Dimethylamino
benzaldehyde
The indole test detects the conversion of tryptophan (present in the media) to indole by the enzyme tryptophanase. Indole is detected by the reaction with the aldehyde group of pdimethylaminobenzaldehyde (the active reagent in Kovac’s and Ehrlich’s reagents) in acid, forming a red complex.
Putrescine is an alkaline amine product of which bacterial enzyme?
A. Arginine decarboxylase
B. Phenylalanine deaminase
C. Ornithine decarboxylase
D. Lysine decarboxylase
C. Ornithine decarboxylase
Putrescine is the amine product of the decarboxylation of ornithine.
Which genera are positive for phenylalanine deaminase?
A. Enterobacter, Escherichia, and Salmonella
B. Morganella, Providencia, and Proteus
C. Klebsiella and Enterobacter
D. Proteus, Escherichia, and Shigella
B. Morganella, Providencia, and Proteus
Phenylalanine deaminase oxidatively deaminates phenylalanine, forming phenylpyruvic acid. When a solution of ferric chloride is added, the iron reacts with phenylpyruvic acid, forming a green-colored complex. Phenylalanine deaminase is found in the genera Morganella, Providencia, and Proteus and is an excellent test to determine if an organism belongs to this group. Rarely, isolates of Enterobacter may be phenylalanine deaminase positive as well.
Which genera of the Enterobacteriaceae are known to cause diarrhea and are considered enteric pathogens?
A. Enterobacter, Klebsiella, Providencia, and Proteus
B. Escherichia, Salmonella, Shigella, and Yersinia
C. Pseudomonas, Moraxella, Acinetobacter, and Aeromonas
D. Enterobacter, Citrobacter, and Morganella
B. Escherichia, Salmonella, Shigella, and Yersinia
Escherichia, Salmonella, Shigella, and Yersinia are responsible for the majority of enteric diarrhea cases attributable to the Enterobacteriaceae family.
Which genera of Enterobacteriaceae are usually nonmotile at 36°C?
A. Shigella, Klebsiella, and Yersinia
B. Escherichia, Edwardsiella, and Enterobacter
C. Proteus, Providencia, and Salmonella
D. Serratia, Morganella, and Hafnia
A. Shigella, Klebsiella, and Yersinia
Shigella spp. and Klebsiella spp. are for the most part nonmotile. Yersinia can be motile at 22°C but is nonmotile at 36°C.
Fever, abdominal cramping, watery stools, and fluid and electrolyte loss preceded by bloody stools 2–3 days before is characteristic of shigellosis
but may also result from infection with:
A. Campylobacter spp.
B. Salmonella spp.
C. Proteus spp.
D. Yersinia spp.
A. Campylobacter spp.
Shigella spp. and Campylobacter spp. are both causes of diarrhea, abdominal pain, fever, and sometimes vomiting. Blood is present in the stools of patients infected with Shigella as a result of invasion and penetration of the bowel. Young children may also exhibit bloody stools when infected with Campylobacter.
A liquid fecal specimen from a three-month-old infant is submitted for microbiological examination. In addition to culture on routine media for
Salmonella and Shigella, this specimen should be routinely:
A. Examined for the presence of Entamoeba hartmanni
B. Examined for the presence of Campylobacter sp.
C. Screened for the detection of enterotoxigenic Escherichia coli
D. Placed in thioglycollate broth to detect Clostridium botulinum
B. Examined for the presence of Campylobacter sp.
Campylobacter continues to be the most common enteric pathogen isolated from patients with diarrhea. Routinely fecal specimens should be cultured for Salmonella, Shigella and Campylobacter. Fecal specimens are not routinely cultured for enterotoxaemia E. coli or C. outline. E. Hartman is a non-pathogenic parasite and does not cause diarrhea.
Cold enrichment of feces (incubation at 4°C) in phosphate-buffered saline prior to subculture onto enteric media enhances the recovery of:
A. Enterotoxigenic E. coli
B. Salmonella paratyphi
C. Hafnia alvei
D. Yersinia enterocolitica
D. Yersinia enterocolitica
Cold enrichment is especially useful when specimens contain large numbers of normal flora that are sensitive to prolonged exposure to near-freezing temperature. In addition to Yersinia, the technique has been used to enhance recovery of Listeria monocytogenes from specimens containing other bacteria.
Infection of the urinary tract is most frequently associated with:
A. Staphylococcus aureus
B. Escherichia coli
C. Enterococcus faecalis
D. Serratia marcescens
B. Escherichia coli
More than 80% of uncomplicated UTIs are caused by Escherichia coli
Which one of the following genera is among the least biochemically reactive members of the Enterobacteriaceae?
A. Proteus
B. Pseudomonas
C. Citrobacter
D. Shigella
D. Shigella
Shigella is lactose negative, most species do not produce gas, are VP, urea, lysine decarboxylase and citrate negative, and they are non motile.
Which of the following organisms can grow in the small bowel and cause diarrhea in children, traveler’s diarrhea, or a severe cholera-like syndrome
through the production of enterotoxins?
A. Yersinia enterocolitica
B. Escherichia coli
C. Salmonella typhi
D. Shigella dysenteriae
B. Escherichia coli
E. coli can produce several different types of toxins that result in different gastroenteritis and manifestations.
A 25-year-old man who had recently worked as a steward on a transoceanic gram ship presented to the emergency room with high fever, diarrhea and prostration. Axillary lymph nodes were hemorrhagic and enlarged. A Wayson stain of the aspirate showed bacilli that were
bipolar, resembling safety pins. The most likely identification of this organism is:
A.Brucella melitensis
B.Streptobacillus moniliformis
C. Spirillum minus
D. Yersinia pestis
D. Yersinia pestis
Yersinia pestis is classically described as having a “safety pin” appearance on Wayson’s stain. This patient’s presentation is classic for bubonic plague.
Enterobacter sakazakii can best be differentiated from Enterobacter cloacae by which of the following characteristics?
A. Yellow pigmentation and negative sorbitol fermentation
B. Pink pigmentation and positive arginine dihydrolase
C. Yellow pigmentation and positive urease
D. H2S production on TSI
A. Yellow pigmentation and negative sorbitol fermentation
E. sakazakii is called a yellow-pigmented E. cloacae and is best differentiated from E. cloacae by sorbitol fermentation (95% positive for E. cloacae and 0% for E. sakazakii). In addition, E. cloacae is usually positive for urease and malonate (65% and 75%, respectively) and E. sakazakii is usually negative (1% and <20%, respectively). Both species are usually motile and arginine dihydrolase positive.
Which single test best separates Klebsiella oxytoca from K. pneumoniae?
A. Urease
B. Sucrose
C. Citrate
D. Indole
D. Indole
K. oxytoca and K. pneumoniae are almost identical biochemically except for the ability to produce indole. Both organisms are usually positive for urease, sucrose, and citrate. However, K. oxytoca is indole positive and K. pneumoniae is indole negative.
The Shiga-like toxin (verotoxin) is produced mainly by which
Enterobacteriaceae?
A. Klebsiella pneumoniae
B. Escherichia coli
C. Salmonella typhimurium
D. Enterobacter cloacae
B. Escherichia coli
Strains of E. coli that produce one or both of the Shiga-like toxins (SLT I and SLT II) can cause bloody diarrhea (hemorrhagic colitis). In the United States, E. coli strain O157:H7 is the serotype most often associated with hemorrhagic colitis.
A leg-wound culture from a hospitalized 70-year-old diabetic man grew motile, lactose-negative colonies on MacConkey agar. Given the following
biochemical reactions at 24 hours, what is the most probable organism?
H2S (TSI) = Neg
MR = Neg
DNase = +
Urease = Neg
Phenylalanine deaminase = Neg
Orthinine and lysine decarboxylase = +
Arginine decarboxylase = Neg
Gelatine hydrolysis = +
Indole = Neg
VP = +
Citrate = +
A. Proteus vulgaris
B. Serratia marcescens
C. Proteus mirabilis
D. Enterobacter cloacae
B. Serratia marcescens
S. marcescens has been implicated in numerous nosocomial infections and is recognized as an important pathogen with invasive properties. Gelatin hydrolysis and DNase are positive for both the Proteus spp. and Serratia, but the negative urease and phenylalanine deaminase are differential.
Three blood cultures taken from a 30-year-old cancer patient receiving chemotherapy and admitted with a urinary tract infection grew lactosenegative, motile, gram-negative rods prior to antibiotic therapy. Given the
following biochemical reactions, which is most likely organism?
H2S (TSI) = +
VP = Neg
DNase = +
Gelatine hydrolysis = +
Orthinine and lysine decarboxylase = Neg
Indole = +
Citrate = Neg
Phenylalanine deaminase = +
MR = +
Urease = +
A. Proteus vulgaris
B. Proteus mirabilis
C. Serratia marcescens
D. Klebsiella pneumoniae
A. Proteus vulgaris
Although P. mirabilis is more frequently recovered from patients with urinary tract infections, P. vulgaris is commonly recovered from immunosuppressed patients. P. mirabilis is indole negative and ornithine decarboxylase positive but otherwise is very similar to P. vulgaris.
Plesiomonas shigelloides is a relatively new member of the family Enterobacteriaceae. What characteristic separates it from other members of the Enterobacteriaceae?
A. It is oxidase positive
B. It ferments glucose
C. It produces pyocyanin
D. It requires 10% carbon dioxide for growth
A. It is oxidase positive
Enterobacteriaceae ferments glucose and are oxidase negative. . Pleisomonas was a member of the Vibrio family in part because it is oxidase positive. However it was moved to the Enterobacteriaceae despite its positive oxidase reaction.
Which tests are most appropriate to differentiate between Pseudomonas
aeruginosa and Pseudomonas putida?
A. Oxidase, motility, pyoverdin
B. Oxidase, motility, lactose
C. Oxidase, ONPG, DNase
D. Mannitol, nitrate reduction, growth at 42°C
D. Mannitol, nitrate reduction, growth at 42°C
Pseudomonas aeruginosa: Positive for mannitol, nitrate reduction and growth at 42C
Pseudomonas putida: Negative for mannitol, nitrate reduction and growth at 42C
Which Pseudomonas is usually associated with a lung infection related to cystic fibrosis?
A. P. fluorescens
B. P. aeruginosa
C. P. putida
D. Burkholderia pseudomallei
B. P. aeruginosa
P. aeruginosa is often recovered from the respiratory secretions of cystic fibrosis patients. If the patient is chronically infected with the mucoid strain of P. aeruginosa, the biochemical identifi cation is very diffi cult. The mucoid strain results from production of large amounts of alginate, a polysaccharide that surrounds the cell.
Which of the listed Pseudomonas spp. is associated with the following virulence factors: exotoxin A, endotoxins, proteolytic enzymes,
antimicrobial resistance, and production of alginate?
A. P. fluorescens
B. P. putida
C. P. stutzeri
D. P. aeruginosa
D. P. aeruginosa
P. aeruginosa is highly resistant to many antimicrobial drugs as well as being one of the most often cultured opportunistic organisms. This virulence factor allows for many nosocomial infections such as those of the urinary tract, wounds (burn patients), bacteremia, respiratory tract, and CNS.
Which organism is associated with immunodeficiency syndromes and melioidosis (a glanders-like disease in Southeast Asia and northern
Australia)?
A. Pseudomonas aeruginosa
B. Pseudomonas stutzeri
C. Pseudomonas putida
D. Burkholderia pseudomallei
D. Burkholderia pseudomallei
B. pseudomallei produces wrinkled colonies resembling P. stutzeri. Infections are usually asymptomatic and can be diagnosed only by serological methods. The organism exists in soil and water in an area of latitude 20° north and south of the equator (mainly in Thailand and Vietnam). Thousands of U.S. military personnel were infected with these bacteria during the 1960s and 1970s. The disease may reactivate many years after exposure and has been called the “Vietnamese time bomb.”
Cetrimide agar is used as a selective isolation agar for which organism?
A. Acinetobacter spp.
B. Pseudomonas aeruginosa
C. Moraxella spp.
D. Stenotrophomonas maltophilia
B. Pseudomonas aeruginosa
Cetrimide (acetyl trimethyl ammonium bromide) agar is used for the isolation and identification of P. aeruginosa. With the exception of P. fluorescens, the other pseudomonads are inhibited along with related nonfermentative bacteria.
A community hospital microbiology laboratory is processing significant
numbers of stool cultures because of an outbreak of diarrhea following heavy rains and flooding in the country. A media that should be
incorporated in the plating protocol is:
A. Colistin nalidixic acid for Listeria
B. MacConkey agar with sorbitol for Campylobacter
C. Mannitol salt agar for Enterococcus species
D. Thiosulfate citrate bile salts sucrose for Vibrio species
D. Thiosulfate citrate bile salts sucrose for Vibrio species
Thiosulfate citrate bile salts agar is a selective media for Vibrio and it also differentiates sucrose fermenting species such as V. cholerae and V. alginolyticus.
“Rice water” stool often contains:
A. Pure culture of Vibrio cholerae
B. Toxigenic Clostridium botulinum
C. Toxigenic Staphylococcus aureus
D. Undigested aflatoxin-contaminated rice
A. Pure culture of Vibrio cholerae
A blood culture bottle with macroscopic signs of growth is Gram stained and the technician notes small, curved gram-negative bacilli resembling
“gull wings.” It is subcultured to blood and chocolate agar, and incubated aerobically and anaerobically. After 24 hours, no growth is apparent. The
next step should be to:
A. Subculture the bottle, and incubate in microaerophilic conditions
B. Assume the organism is nonviable, and ask for repeat specimen
C. Utilize a pyridoxal disk to detect Aeromonas
D. Subculture the bottle to a medium containing X and V factors
A. Subculture the bottle, and incubate in microaerophilic conditions
Campylobacter are gram negative, curved bacilli that require microaerophilic conditions for growth.
Which atmospheric condition is needed to recover Campylobacter spp. from specimens inoculated onto a Campy -selective agar at 35°C–37°C and 42°C?
A. 5% O2, 10% CO2, and 85% N2
B. 20% O2, 10% CO2, and 70% N2
C.20% O2, 20% CO2, and 60% N2
20% O2, 5% CO2, and 75% N2
A. 5% O2, 10% CO2, and 85% N2
A gastroenterologist submits a gastric biopsy from a patient with a peptic ulcer. To obtain presumptive evidence of Helicobacter pylori, a portion of
the specimen should be added to which media?
A. Urea broth
B. Tetrathionate
C. Selenite
D. Tryptophan
A. Urea broth
Helicobacter pylori produce large amounts of extracellular urease and are positive for urea within 2 hours.
Which group of tests best differentiates Helicobacter pylori from C. jejuni?
A. Catalase, oxidase, and Gram stain
B. Catalase, oxidase, and nalidixic acid sensitivity
C. Catalase, oxidase, and cephalothin sensitivity
D. Urease, nitrate, and hippurate hydrolysis
D. Urease, nitrate, and hippurate hydrolysis
H. pylori: positive for urease; negative for nitrate reduction and hippurate hydrolysis
C. jejuni: negative for urease; positive for nitrate reduction and hippurate hydrolysis
Smooth gray colonies showing no hemolysis are recovered from an infected cat scratch on blood and chocolate agar but fail to grow on MacConkey agar. The organisms are gram-negative pleomorphic rods that are both catalase and oxidase positive and strongly indole positive.
The most likely organism is:
A. Capnocytophaga spp.
B. Pasteurella spp.
C. Proteus spp.
D. Pseudomonas spp.
B. Pasteurella spp.
Pasteurella multocida (P. canis) is part of the normal mouth flora of cats and dogs and is frequently recovered from wounds infl icted by them. It produces large amounts of indole and therefore an odor resembling colonies of E. coli. Pseudomonas spp. are also catalase and oxidase positive but can be ruled out because they grow on MacConkey agar and do not produce indole.
Which of the following amino acids are required for growth of Francisella tularensis?
A. Leucine and ornithine
B. Arginine and lysine
C. Cysteine and cystine
D. Histidine and tryptophan
C. Cysteine and cystine
F. tularensis is a fastidious gram-negative rod that is best recovered from lymph node aspirates and tissue biopsies. It is oxidase negative, nonmotile, and inert biochemically. Cysteine blood agar is the medium of choice, but F. tularensis will grow on commercially prepared chocolate agar because it contains X factor and is supplemented with a growth enrichment (IsoVitaleX) that contains cysteine. F. tularensis may not grow well on MacConkey agar.
Which of the following plates should be used in order to identify Haemophilus haemolyticus and Haemophilus parahaemolyticus?
A. Sheep blood agar and chocolate agar
B. Horse blood agar and Mueller–Hinton agar with X and V strips
C. Brain–heart infusion agar with sheep red cells added
D. Chocolate agar and Mueller–Hinton agar with X factor added
B. Horse blood agar and Mueller–Hinton agar with X and V strips
Production of β-hemolysis is used to distinguish these two species from other Haemophilus with the same X and V requirements. Horse blood agar furnishes X factor and, when supplemented with yeast extract, supports the growth of Haemophilus spp. Sheep blood agar is not used because it contains growth inhibitors for some Haemophilus spp.
Which Haemophilus species is difficult to isolate and recover from genital ulcers and swollen lymph nodes?
A. H. aphrophilus
B. H. ducreyi
C. H. haemolyticus
D. H. parahaemolyticus
B. H. ducreyi
H. ducreyi requires exogenous X factor and causes genital lesions referred to as “soft chancres.”
Gram-negative bacilli, catalase positive, lactose negative, xylose positive:
A. H. aegypticus
B. H. ducreyi
C. H. parainfluenzae
D. H. influenzae
D. H. influenzae
“Clue cells” are seen on a smear of vaginal discharge obtained from an 18-year-old female emergency department patient. This finding, alongwith a fishy odor (amine) after the addition of 10% KOH, suggests
bacterial vaginosis caused by which organism?
A. Staphylococcus epidermidis
B. Streptococcus agalactiae
C. Gardnerella vaginalis
D. Escherichia coli
C. Gardnerella vaginalis
A gram-negative, fastidious bacillus that has been isolated from air conditioning towers:
A. Brucella abortus
B. Edwardsiella tarda
C. Legionella pneumophila
D. Proteus vulgaris
C. Legionella pneumophila
During the summer break, several middle-aged elementary school teachers from the same school district attended a 3-day seminar in Chicago. Upon returning home, three female teachers from the group were hospitalized with pneumonia, flu-like symptoms, and a nonproductive cough. Routine testing of sputum samples revealed normal flora. Further testing using BCYE agar with L-cysteine and α-
ketoglutarate in 5% CO2 produced growth of opaque colonies that stained faintly, showing thin gram-negative rods. What is the most likely
identification?
A. Legionella pneumophila
B. Haemophilus influenzae
C. Eikenella corrodens
D. Streptococcus pneumoniae
A. Legionella pneumophila
L. pneumophila is the cause of pneumonia and can occur as part of an epidemic sporadically or nosocomially, or may be community acquired. The appearance of mottled, cut-glass colonies on buffered CYE agar under low power and the use of a direct immunofluorescence technique on sputum samples determine the presence of L. pneumophila.
The most common environmental sites for recovery are shower heads, faucets, water tanks, and air-conditioning systems.
“Chocolate cake” or “burnt chocolate” smell:
A.Burkholderia cepacia
B. Pasteurella multocida
C. Proteus spp.
D. Pseudomonas aeruginosa
C. Proteus spp.
Fruity or grapelike smell, corn tortilla-like odor:
A. Burkholderia cepacia
B. Pasteurella multocida
C. Proteus spp.
D. Pseudomonas aeruginosa
D. Pseudomonas aeruginosa
Musty or mushroom odor:
A. Burkholderia cepacia
B. Pasteurella multocida
C. Proteus spp.
D. Pseudomonas aeruginosa
B. Pasteurella multocida
Smell of ammonium cyanide (almond-like):
A. Eikenella corrodens
B. Chromobacterium violaceum
C. Haemophilius influenzae
D. Stenotrophomonas maltophilia
B. Chromobacterium violaceum
Oxidase positive, urease negative:
A. B. pertussis
B. B. parapertussis
C. B. bronchiseptica
D. None of these
A. B. pertussis
Oxidase and urease positive:
A. B. pertussis
B. B. parapertussis
C. B. bronchiseptica
D. None of these
C. B. bronchiseptica
Oxidase negative, urease positive:
A. B. pertussis
B. B. parapertussis
C. B. bronchiseptica
D. None of these
B. B. parapertussis
Large gram-positive spore-forming rods growing on blood agar as large, raised, β-hemolytic colonies that spread and appear as frosted green-gray glass are most likely:
A. Pseudomonas spp.
B. Bacillus spp.
C. Corynebacterium spp.
D. Listeria spp.
B. Bacillus spp.
The only spore former listed is the Bacillus spp., which grow as large, spreading colonies on blood agar plates. Pseudomonas spp. are gram-negative rods; Corynebacterium spp. appear as small, very dry colonies on BAP; Listeria spp. appear as very small β-hemolytic colonies on BAP, resembling Streptococcus species.
Bacillus anthracis and Bacillus cereus can best be differentiated by which
tests?
A. Motility and β-hemolysis on a blood agar plate
B. Oxidase and β-hemolysis on a blood agar plate
C. Lecithinase and glucose
D. Lecithinase and catalase
A. Motility and β-hemolysis on a blood agar plate
Both species of Bacillus are catalase and lecithinase positive and produce acid from glucose. B. cereus is β-hemolytic and motile, but B. anthracis is neither.
A suspected Bacillus anthracis culture obtained from a wound specimen produced colonies that had many outgrowths (Medusa-head appearance),but were not β-hemolytic on sheep blood agar. Which test
should be performed next?
A. Penicillin (10-unit) susceptibility test
B. Lecithinase test
C. Glucose test
D. Motility test
A. Penicillin (10-unit) susceptibility test
The best differentiating test to perform on a suspected B. anthracis culture is the 10-unit penicillin disk test. B. anthracis is susceptible but other Bacillus spp. are not.
Which is the specimen of choice for proof of food poisoning by Bacillus cereus
A. Sputum
B. Blood
C. Stool
D. Food
D. Food
The best specimen is the suspected food itself. Stool cultures are not useful because B. cereus is part of the normal fecal flora. The suspected food can be the source of food poisoning by B. cereus if 100,000 or greater organisms per gram of infected food are demonstrated.
Which Clostridium species is most often recovered from a wound infection with gas gangrene?
A. C. sporogenes
B. Clostridium sordellii
C. C. novyi
D. C. perfringens
D. C. perfringens
Wounds infected with clostridia are characterized by invasion and liquefactive necrosis of muscle tissue with gas formation. The most frequent isolate is C. perfringens followed by C. novyi and C. septicum.
A gram-positive spore-forming bacillus growing on sheep-blood agar anaerobically produces a double zone of β-hemolysis and is positive for lecithinase. What is the presumptive identification?
A. Bacteroides ureolyticus
B. Bacteroides fragilis
C. Clostridium perfringens
D. Clostridium difficile
C. Clostridium perfringens
C. perfringens produces a double zone of β-hemolysis on blood agar, which makes identification relatively easy. The inner zone of complete hemolysis is caused by a θ-toxin and the outer zone of incomplete hemolysis is caused by an α-toxin (lecithinase activity).
The Bacteroides spp. are gram-negative bacilli, and C. diffi cile is lecithinase negative and does not produce a double zone of β-hemolysis.
Egg yolk agar is used to detect which enzyme produced by Clostridium species?
A. Lecithinase
B. β-Lactamase
C. Catalase
D. Oxidase
A. Lecithinase
Egg yolk agar (modifi ed McClung’s or neomycin egg yolk agar) is used to determine the presence of lecithinase activity, which causes an insoluble, opaque, whitish precipitate within the agar. Lipase activity is indicated by an iridescent sheen or pearly layer on the surface of the agar.
Which of the following organisms will display lipase activity on egg yolk agar?
A. Clostridium botulinum
B. Clostridium sporogenes
C. Clostridium novyi (A)
D. All of these options
D. All of these options
LIPASE + C. botulinum, C. sporogenes and C. novyi. Lipase is produced by some Clostridium spp. and is seen as an iridescent pearly layer on the surface of the colonies that extends onto the surface of the egg yolk agar medium
surrounding them. C. perfringens, the most frequently isolated Clostridium species, is negative for lipase production.
The classic form of foodborne botulism is characterized by the ingestion of:
A. Spores in food
B. Preformed toxin in food
C. Toxin H
D. All of these options
B. Preformed toxin in food
Foodborne botulism in adults and children is caused by ingestion of the preformed toxin (botulinum toxins A, B, E, and F) in food. The neurotoxins of C. botulinum are protoplastic proteins made during the growing phase and released during lysis of the organisms. Confirmation of botulism is made by demonstration of the toxin in serum, gastric, or stool specimens.
Which mechanism is responsible for botulism in infants caused by
Clostridium botulinum?
A. Ingestion of spores in food or liquid
B. Ingestion of preformed toxin in food
C. Virulence of the organism
D. Lipase activity of the organism
A. Ingestion of spores in food or liquid
Epidemiological studies have demonstrated that infant botulism results from the ingestion of spores via breastfeeding or exposure to honey. Preformed toxin has not been detected in food or liquids taken by the infants. C. botulinum multiplies in the gut of the infant and produces the neurotoxin in situ.
Which test is performed in order to confirm an infection with Clostridium botulinum?
A. Toxin neutralization
B. Spore-forming test
C. Lipase test
D. Gelatin hydrolysis test
A. Toxin neutralization
Definitive identification of C. botulinum is made by the toxin neutralization test for its neurotoxins in serum or feces.
Which spore type and location is found on Clostridium tetani?
A. Round, terminal spores
B. Round, subterminal spores
C. Ovoid, subterminal spores
D. Ovoid, terminal spores
A. Round, terminal spores
Spore appearance and location, along with Gram stain morphology, aids in distinguishing the Clostridium spp.
Round, terminal spores are demonstrated when C. tetani is grown in chopped meat with glucose broth. Recognition of spores is particularly important because C. tetani sometimes appears as gram negative.
Identification of Clostridium tetani is based upon:
A. Gram stain of the wound site
B. Anaerobic culture of the wound site
C. Blood culture results
D. Clinical findings
D. Clinical findings
The culture and Gram stain of the puncture wound site usually does not produce any evidence of C. tetani. The diagnosis is usually based upon clinical findings, which are characterized by spastic muscle contractions, lockjaw, and backward arching of the back caused by muscle contraction.
Which Clostridium spp. causes pseudomembranous colitis or antibioticassociated colitis?
A. C. ramosum
B. C. difficile
C. C. perfringens
D. C. sporogenes
B. C. difficile
C. diffi cile is also implicated in hospital acquired diarrhea and colitis. Clinical testing for C. difficile includes culture and cytotoxin testing. Because culture takes 3 days and will detect nontoxigenic strains that do not cause diarrheal disease, immunoassays using antibodies against either the A toxin or both the A and B toxins are most frequently employed.
Cycloserine–cefoxitin-fructose agar (CCFA) is used for the recovery of:
A. Yersinia enterocolitica
B. Yersinia intermedia
C. Clostridium perfringens
D. Clostridium difficile
D. Clostridium difficile
CCFA is used for recovery of C. diffi cile from stool cultures. Cycloserine and cefoxitin inhibit growth of gram-negative coliforms in the stool specimen. C. difficile ferments fructose, forming acid that, in the presence of neutral red, causes the colonies to become yellow.
Methods other than packaged microsystems used to identify anaerobes include:
A. Antimicrobial susceptibility testing
B. Gas–liquid chromatography (GLC)
C. Special staining
D. Enzyme immunoassay
B. Gas–liquid chromatography (GLC)
Anaerobic bacteria can be identified by analysis of metabolic products using gas–liquid chromatography. Results are evaluated along with Gram staining characteristics, spore formation, and cellular morphology in order to make the identification
A flexible calcium alginate nasopharyngeal swab is the collection device of choice for recovery of which organism from the nasopharynx?
A. Staphylococcus aureus
B. Streptococcus pneumoniae
C. Corynebacterium diphtheriae
D. Bacteroides fragilis
C. Corynebacterium diphtheriae
C. diphtheriae must be recovered from the deep layers of the pseudomembrane that forms in the nasopharyngeal area. A flexible calcium alginate nasopharyngeal swab is the best choice for collecting a specimen from the posterior nares and pharynx.
A direct smear from a nasopharyngeal swab stained with Loeffler methylene blue stain showed various letter shapes and deep blue,
metachromatic granules. The most likely identification is:
A. Corynebacterium spp.
B. Nocardia spp.
C. Listeria spp.
D. Gardnerella spp.
A. Corynebacterium spp.
Corynebacterium spp. are part of the normal upper respiratory tract flora. Organisms display typical pleomorphic shapes often resembling letters such as Y or L, and metachromatic granules. Identification of C. diphtheriae, however, requires selective culture media and biochemical testing.
An emergency department physician suspected Corynebacterium diphtheriae when examining the sore throat of a patient. What is the
appropriate media for the culture of the nasopharyngeal swab obtained from the patient?
A. Chocolate agar
B. Thayer–Martin agar
C. Tinsdale medium
D. MacConkey agar
C. Tinsdale medium
Corynebacterium will grow on blood and chocolate agars, but Tinsdale agar is the preferred culture medium because the potassium tellurite in the agar causes C. diphtheriae to produce brown colonies surrounded by a brown halo. The halo effect is seen with C. diphtheriae, C. ulcerans, and C. pseudotuberculosis but not with other Corynebacterium or with other pigmented colonies growing on Tinsdale agar.
Establishing the pathogenicity of a microorganism isolated from a child’s throat and identified as Corynebacterium diphtheriae would depend upon:
A. The morphological appearance as revealed by Gram stain
B.The type of hemolysis on blood agar
C. A positive toxigenicity test
D. The appearance of growth on Tinsdale tellurite agar
C. A positive toxigenicity test
In order to determine if an isolate of Corynebacterium diphtheriae produces toxin, testing for the presence of diphtheria toxin must be performed using methods such as Elek test or PCR.
Which of the following tests should be performed for initial differentiation of Listeria monocytogenes from group B streptococci?
A. Gram stain, motility at room temperature, catalase
B. Gram stain, CAMP test, H2S/TSI
C. Oxidase, CAMP test, glucose
D. Oxidase, bacitracin
A. Gram stain, motility at room temperature, catalase
*Streptococci
Gram positive cocci in chains
Nonmotile
Catalase negative
*Listeria
Gram positive bacilli
Motile
Catalase positive
Culture of a finger wound specimen from a meat packer produced short gram-positive bacilli on a blood agar plate with no hemolysis. Given the
following test results: catalase negative, bottle-brush growth in stab culture, H2S +.
A. Bacillus cereus
B. Listeria monocytogenes
C. Erysipelothrix rhusiopathiae
D. Bacillus subtilis
C. Erysipelothrix rhusiopathiae
E. rhusiopathiae is catalase negative, whereas the other three organisms are catalase positive. E. rhusiopathiae is seen primarily as a skin infection on the fingers of meat and poultry workers. Colonies growing on blood agar are small and transparent, may be either smooth or rough, and are often surrounded by a green tinge. E. rhusiopathiae is characterized by H2S production in the butt of a TSI slant, which differentiates it from other catalase-negative, gram-positive rods.
A non–spore-forming, slender gram-positive rod forming palisades and chains was recovered from a vaginal culture and grew well on tomato
juice agar. The most likely identification is:
A. Lactobacillus spp.
B. Bacillus spp.
C. Neisseria spp.
D. Streptococcus spp.
A. Lactobacillus spp.
Lactobacillus spp. produce both long, slender rods or short coccobacilli that form chains. Lactobacillus spp. are part of the normal flora of the vagina (are not considered a pathogen) and are sometimes confused with the streptococci.
Gram stain of a smear taken from the periodontal pockets of a 30-yearold man with poor dental hygiene showed sulfur granules containing gram-positive rods (short diphtheroids and some unbranched filaments). Colonies on blood agar resembled “molar teeth” in formation. The most likely organism is:
A. Actinomyces israelii
B. Propionibacterium acnes
C. Staphylococcus intermedius
D. Peptostreptococcus anaerobius
A. Actinomyces israelii
A. israelii is part of the normal flora of the mouth and tonsils but may cause upper or lower respiratory tract infections. The sulfur granules are granular microcolonies with a purulent exudate
A gram-positive branching filamentous organism recovered from a sputum specimen was found to be positive with a modified acid-fast stain method. What is the most likely presumptive identification?
A. Bacillus spp.
B. Nocardia spp.
C. Corynebacterium spp.
D. Listeria spp.
B. Nocardia spp.
Nocardia spp. should be suspected if colonies that are partially acid fast by the traditional method are positive with the modifi ed acid-fast method using Kinyoun stain and 1% sulfuric acid as the decolorizing agent. The other organisms listed are negative for acid fast stain.
A gram-positive (gram-variable), beaded organism with delicate
branching was recovered from the sputum of a 20-year-old patient with leukemia. The specimen produced orange, glabrous, waxy colonies on
Middlebrook’s agar that showed partial acid-fast staining with the
modified Kinyoun stain. What is the most likely identification?
A. Rhodococcus spp.
B. Actinomadura spp.
C. Streptomyces spp.
D. Nocardia spp.
D. Nocardia spp.
All of the listed organisms produce mycelium (aerial or substrate), causing them to appear branched when Gram stained, but only the Nocardia spp. are positive for modified acid fast stain. Nocardia is an opportunistic pathogen, and cultures typically have a musty basement odor.
A branching gram-positive, partially acid-fast organism is isolated from a bronchial washing on a 63-year-old woman receiving chemotherapy. The organism does not hydrolyze casein, tyrosine or xanthine. The most
likely identification is:
A. Actinomadura madurae
B. Streptomyces somaliensis
C. Nocardia caviae
D. Nocardia asteroides
D. Nocardia asteroides
Nocarida asteroides are partially acid fast and do not hydrolyze the substrates casein, tyrosine or xanthine.
Mycobacteria stained by the Ziehl–Neelsen or Kinyoun methods with methylene blue counterstain are seen microscopically as:
A. Bright red rods against a blue background
B. Bright yellow rods against a yellow background
C. Orange-red rods against a black background
D. Bright blue rods against a pink background
A. Bright red rods against a blue background
The carbolfuchsin (fuchsin with phenol) stains the mycobacteria red and does not decolorize after the acid–alcohol is added. The background and any other bacterial elements will decolorize and are counterstained blue by the methylene blue.
Which is the most appropriate nonselective medium for recovery of mycobacteria from a heavily contaminated specimen?
A. Löwenstein–Jensen agar
B. Middlebrook 7H10 agar
C. Petragnani’s agar
D. American Thoracic Society medium
C. Petragnani’s agar
All four media contain malachite green as an inhibitory agent of nonmycobacteria, but Petragnani’s medium contains a higher concentration (0.052 g/dL) than Löwenstein– Jensen (0.025 g/dL), Middlebrook 7H10 (0.0025 g/dL), or American Thoracic Society medium (0.02 g/dL). The last is used for normally sterile specimens, such as from CSF and bone marrow.
A lymph node biopsy obtained from a 30-year-old male patient was submitted to the microbiology laboratory for a culture and AFB smear for
mycobacteria. The specimen was fixed in formalin. This specimen should be:
A. Accepted for AFB smear and cultured
B. Rejected
C. Held at room temperature for 24 hours and then cultured
D. Cultured for anaerobes only
B. Rejected
Specimens submitted for culture and recovery of any bacteria should be submitted without fixatives.
All of the following Mycobacterium spp. produce the enzyme required to
convert niacin to niacin ribonucleotide except:
A. M. kansasii
B. M. tuberculosis
C. M. avium–intracellulare complex
D. M. szulgai
B. M. tuberculosis
Niacin production is common to all mycobacteria. However, the niacin accumulates as a water-soluble metabolite in the culture medium when the organism cannot form niacin ribonucleotide. M. tuberculosis, M. simiae, and some strains of M. marinum, M. chelonae, and M. bovis lack the enzyme and therefore are called niacin positive because of the accumulation of niacin detected in the test medium.
Acid-fast staining of a smear prepared from digested sputum showed slender, slightly curved, beaded, red mycobacterial rods. Growth on Middlebrook 7H10 slants produced buff-colored microcolonies with a serpentine pattern after 14 days at 37°C. Niacin and nitrate reduction tests were positive. What is the most probable presumptive identification?
A. Mycobacterium tuberculosis
B. Mycobacterium ulcerans
C. Mycobacterium kansasii
D. Mycobacterium avium–intracellulare complex
A. Mycobacterium tuberculosis
M. tuberculosis is positive for niacin accumulation, while the other three species are niacin negative. A serpentine pattern of growth indicates production of cording factor, a virulence factor for M. tuberculosis.
Which organism, associated with tuberculosis in cattle, causes
tuberculosis in humans, especially in regions where dairy farming is prevalent?
A. Mycobacterium avium–intracellulare complex
B. Mycobacterium kansasii
C. Mycobacterium marinum
D. Mycobacterium bovis
D. Mycobacterium bovis
M. bovis is also called the bovine tubercle bacillus. A nonvirulent strain, bacillus Calmette– Guérin (BCG), is used as a tuberculosis vaccine throughout the world. Infections with M. bovis resemble infections caused by M. tuberculosis and are seen in circumstances where there is close contact between humans and cattle.
Growth inhibition by thiophene-2-carboxylichydrazide (T2H) is used to differentiate M. tuberculosis from which other Mycobacterium sp.:
A. M. bovis
B. M. avium–intracellulare complex
C. M. kansasii
D. M. marinum
A. M. bovis
M. bovis and M. tuberculosis are very similar biochemically, and some strains of M. bovis also accumulate niacin. The T2H test differentiates M. tuberculosis from M. bovis. M. tuberculosis is not inhibited by T2H
Which of the following Mycobacterium spp. is best differentiated by the rapid hydrolysis of Tween 80?
A. M. fortuitum
B. M. chelonae
C. M. kansasii
D. M. gordonae
C. M. kansasii
M. kansasii hydrolyses Tween 80 more rapidly than the other species (within 3–6 hours).
Which M. avium complex (MAC) organism is the most frequently isolated mycobacterium from AIDS patients?
A. M. avium
B. M. intracellulare
C. M. scrofulaceum
D. M. bovis
A. M. avium
More than 90% of MAC organisms that are isolated from AIDS patients are M. avium. These are distinguished from M. intraceulluare by NATs.
Which nonpathogenic Mycobacterium specie is isolated most often from
clinical specimens and is called the “tapwater bacillus”?
A. M. kansasii
B. M. avium–intracellulare complex
C. M. leprae
D. M. gordonae
D. M. gordonae
M. gordonae is a nonpathogen, scotochromogen, and rapid grower (7 days at 37°C). Rarely, it is implicated in opportunistic infections in patients with shunts, prosthetic heart values, or hepatoperitoneal disease. The other three species are pathogenic mycobacteria.
Which mycobacterium is associated with Crohn’s disease?
A. M. marinum
B. M. paratuberculosis
C. M. avium
D. M. gordonae
B. M. paratuberculosis
M. paratuberculosis is known to cause an ulcerative intestinal disease with chronic diarrhea in cattle known as Johne’s disease. While M. paratuberculosis has been isolated from the intestines of humans with Crohn’s disease, the organism has not yet been proven to cause ileitis in humans.
Which of the following Mycobacterium species is diagnosed by means
other than culture?
A. M. leprae
B. M. bovis
C. M. canetti
D. M. avium
A. M. leprae
M. leprae and M. microti are different from all other mycobacteria because they cannot be cultured in vitro.
Biopsies from nodules and plaques of skin that show numerous AFB are presumptively diagnosed as positive for M. leprae. Confirmatory identification is made by nucleic acid testing (NAT) using PCR.
Which of the following Mycobacterium spp. would be most likely to grow on a MacConkey agar plate?
A. M. chelonae–fortuitum complex
M. ulcerans
M. marinum
M. avium–intracellulare complex
A. M. chelonae–fortuitum complex
Mycobacteria growing on MacConkey agar are usually nonpathogens. M. chelonae and M. fortuitum are both nonpathogenic rapid growers that will grow on MacConkey agar (with no crystal violet) within 5 days.
Spirochetes often detected in the hematology laboratory, even before the physician suspects the infection, are:
A. Borrelia spp.
B. Treponema spp.
C. Campylobacter spp.
D. Leptospira spp.
A. Borrelia spp.
Borrelia spp. are often seen on Wright’s-stained smears of peripheral blood as helical bacteria with 3–10 loose coils. They are gram negative but stain well with Giemsa’s stain.
Which of the following organisms is the cause of Lyme disease?
A. Treponema pallidum
B. Neisseria meningitidis
C. Babesia microti
D. Borrelia burgdorferi
D. Borrelia burgdorferi
Lyme disease may result in acute arthritis and meningitis and is caused by B. burgdorferi.
The diagnostic method most commonly used for the identification of Lyme disease is:
A. Serology
B. Culture
C. Gram stain
D. Acid-fast stain
A. Serology
Serological analysis using immunofluorescence or an enzyme immunoassay is the method of choice for diagnosis of Lyme disease.
Routine laboratory testing for Treponema pallidum involves:
A. Culturing
B. Serological analysis
C. Acid-fast staining
D. Gram staining
B. Serological analysis
Serological tests of the patient’s serum for evidence of syphilis are routinely performed, but culturing is not because research animals must be used for inoculation of the suspected spirochete. T. pallidum does not stain by either the Gram or acid-fast technique.
Which procedure is appropriate for culture of genital specimens in order to recover Chlamydia spp.?
A. Inoculate cycloheximide-treated McCoy cells
B. Plate onto blood and chocolate agar
C. Inoculate into thioglycollate (THIO) broth
D. Plate onto modified Thayer–Martin agar within 24 hours
A. Inoculate cycloheximide-treated McCoy cells
Chlamydiae are strict intracellular organisms and must be cultured using living cells. Direct smears can also be made at the time of culture. Staining cells with iodine may reveal the characteristic reddish-brown inclusions sometimes seen in Chlamydia infections. Fluorescein-conjugated monoclonal antibodies may be used to identify the organisms in infected cells.
Which is the test of choice for the confirmation of Chlamydia trachomatis infection in urine?
A. Enzyme immunoassay antigen testing
B. PCR molecular testing
C. Culture using McCoy and Hela cells
D. Microimmunofluorescence (MIF) test
B. PCR molecular testing
PCR is both sensitive and specific and may be performed on urine.
Primary atypical pneumonia is caused by:
A. Streptococcus pneumoniae
B. Mycoplasma pneumoniae
C. Klebsiella pneumoniae
D. Mycobacterium tuberculosis
B. Mycoplasma pneumoniae
A common cause of respiratory tract illness, M. pneumoniae, generally causes a self limited infection (3–10 days) and usually does not require antibiotic therapy. M. pneumoniae can be cultured from the upper and lower respiratory tracts onto specially enriched (diphasic) media, but is most frequently diagnosed by the change in antibody titer from acute to convalescent serum using enzyme immunoassay or other serological methods.
Which organism typically produces “fried-egg” colonies on agar within 1– 5 days of culture from a genital specimen?
A. Mycoplasma hominis
B. Borrelia burgdorferi
C. Leptospira interrogans
D. Treponema pallidum
A. Mycoplasma hominis
Genital mycoplasmas (M. hominis and Ureaplasma urealyticum) are grown on specific agars. M. hominis is grown on “M” agar containing arginine and phenol red. Colonies of mycoplasma are 50–300 μm in diameter and display a “fried-egg” appearance with red holes.
Which test is the most reliable for the detection of Mycoplasma
pneumoniae in serum and for the confirmation of diagnosis?
A. EIA testing and direct antigen testing
B. Cold agglutinin testing using Group O RBCs
C. Culture on SP4 glucose broth with arginine
D. Complement fixation
A. EIA testing and direct antigen testing
Adults may fail to produce an IgM response especially in recurrent infections, so the best confirmatory approach is a combination of EIA and direct antigen testing.
The manganous chloride–urea test is used for the identification of which organism?
A. Mycoplasma pneumoniae
B. Ureaplasma urealyticum
C. Bacillus cereus
D. Borrelia burgdorferi
B. Ureaplasma urealyticum
U. urealyticum is the only human mycoplasma that hydrolyzes urea. The manganous chloride–urea test utilizes manganous chloride (MnCl2) in the presence of urea. Urease produced by the organism hydrolyzes the urea to ammonia. This reacts with MnCl2 forming manganese oxide, which is insoluble and forms a dark brown precipitate around the colonies. The reaction is observed under a dissecting microscope and is a rapid test for the identifi cation of U. urealyticum.
Which of the following organisms are transmitted to animals and humans 2/2
after a tick bite?
A. Leptospira
B. Chlamydia and Mycoplasma spp.
C. Neisseria sicca
D. Ehrlichia and Anaplasma spp.
D. Ehrlichia and Anaplasma spp.
Ehrlichia and Anaplasma spp. are intracellular bacteria and are the causative agents of human monocytotropic ehrlichiosis (HME) and human granulocytotropic anaplasmosis (HGA). The organisms infect humans, dogs, and cattle through the bite of an infected Ixodes tick which also transmits Borrelia spp., causing Lyme disease.
For which clinical specimens is the KOH direct mount technique for examination of fungal elements used?
A. Skin
B. CSF
C. Blood
D. Bone marrow
A. Skin
A solution of 10% KOH is used for contaminated specimens such as skin, nail scrapings, hair, and sputum to clear away background debris that may resemble fungal elements. Normally sterile specimens (CSF, blood, and bone marrow) do not require KOH for clearing.
The mycelial form ofHistoplasma capsulatumseen on agar resembles:
A. Sepedonium spp.
B. Penicillium spp.
C. Sporothrix spp.
D. Coccidioides spp.
A. Sepedonium spp.
Sepedonium spp. are saprophytic molds that do not have a yeast phase and produce large spherical tuberculate macroconidia like H. capsulatum. Histoplasmosis is a chronic granulomatous infection primarily found in the lungs that invades the reticuloendothelial system. Infection occurs via spores released from decaying bird or chicken droppings that
are inhaled when disturbed.
The most useful finding for prompt, presumptive identification of C. albicans is its:
A. Failure to assimilate sucrose
B. Feathering on EMB
C. Production of chlamydospores
D. Production of germ tubes
D. Production of germ tubes
Essentially all strains of Candida albicans produce germ tubes within 2 hours of incubation at 37°C in serum.
Germ tube formation is seen with which two yeasts?
A. C. albicans, C. neoformans
B. C. albicans, C. parapsilosis
C. C. glabrata, C. parapsilosis
D. C. albicans, C. dubliniensis
D. C. albicans, C. dubliniensis
The formation of arthroconidia is NOT an important characteristic in the identification of:
A. Coccidioides
B. Geotrichum
C. Trichosporon
D. Sporothrix
D. Sporothrix
Sporothrix is the sole member of the list that does not produce arthroconidia.
A black pigment produced by colonies growing on bird seed agar is due to:
A. Urease
B. Phenol oxidase
C. Sucrose assimilation
D. Arthroconidia production
B. Phenol oxidase
Phenol oxidase breaks down the substrate found in niger seeds producing melanin. This result is characteristic of C. neoformans.
What are the optimal temperature and incubation time before a fungal blood culture is reported as negative?
A. 37°C; 21 days
B. 37°C; 7 days
C. 30°C; 21 days
D. 30°C; 7 days
C. 30°C; 21 days
Which group of molds can be ruled out when septate hyphae are observed in a culture?
A. Dematiaceous
B. Zygomycetes
C. Dermatophytes
D. Dimorphic molds
B. Zygomycetes
Tinea versicolor is a skin infection caused by:
A. Malassezia furfur
B. Trichophyton rubrum
C. Trichophyton schoenleinii
D. Microsporum gypseum
A. Malassezia furfur
M. furfur has a worldwide distribution and causes a superficial, brownish, dry, scaly patch on the skin of light-skinned persons and lighter patches on persons with dark skin.
Dry, horny, platelike lesions or SCALES are associated with:
A. Dermatophytes (tinea)
B. Sporothrix schenckii
C. Mycobacterium marinum
D. Varicella-zoster virus
A. Dermatophytes (tinea)
A patient with a Wood’s lamp–positive, dermatophytic infection has a skin scraping taken for culture. The organism grows on SDA agar with a light-tan front and salmon-colored reverse. Microscopically the organism
produces rare distorted macroconidia and rare microconidia. Additionally,
there was no growth on sterile rice media. What is the most likely organism?
A. Microsporum canis
B. Microsporum gypseum
C. Microsporum audouinii
D. Epidermophyton floccosum
C. Microsporum audouinii
Historically, the differentiation of dermatophytes was accomplished using a variety of morphologic characteristics and growth characteristics. The characteristics listed support the identification of Microsporum audouinii. The most suggestive of these characteristics is the rare distorted macroco- nidia and rare microconidia.
The Hair Baiting Test is used to differentiate which two species
ofTrichophytonthat produce red colonies on Sabouraud agar plates?
A. T. mentagrophytes and T. rubrum
B. T. tonsurans and T. schoenleinii
C. T. verrucosum and T. rubrum
D. T. tonsurans and T. violaceum
A. T. mentagrophytes and T. rubrum
T. mentagrophytes may produce a deep red pigment seen through the reverse side of the agar plate that resembles the cherry-red pigment produced by T. rubrum.
However, T. mentagrophytes can be differentiated by its ability to invade the hair shaft. T. rubrum grows on the surface of the hair but does not penetrate the shaft.
Adding specimen scrapings to 10% KOH to show the presence of SCLEROTIC BODIES that resemble COPPER PENNIES is useful in the diagnosis of:
A. Chromoblastomycosis
B. Phaeohyphomycosis
C. Mycetomas
D. Zygomycosis
A. Chromoblastomycosis
A thermally dimorphic fungus shows a filamentous mold form with TUBERCULATE MACROCONIDIA at room temperature, and a yeast form
above 35°C. Which organism best fits this description?
A. Histoplasma capsulatum
B. Paracoccidioides brasiliensis
C. Candida albicans
D. Coccidioides immitis
A. Histoplasma capsulatum
A KOH preparation of respiratory secretions of a 78- year-old man reveals large, spherical, thick-walled yeast cells 8 to 15 um in diameter, usually with a single bud that is connected to the parent cell by a broad base.
Which fungus will likely be isolated from the culture?
A. Coccidioides immitis
B. Blastomyces dermatitidis
C. Histoplasma capsulatum
D. Paracoccidioides brasiliensis
B. Blastomyces dermatitidis
Blastomyces dermatitidis is endemic to North America, specifi cally the Mississippi river valley. When seen in tissue samples it appears as large, spherical, thick-walled yeast cells 8 to 15 um in diameter, usually with a single bud that is connected to the parent cell by a broad base.
The yeast form of which dimorphic mold shows a large parent yeast cell surrounded by smaller budding yeast cells?
A. Paracoccidioides brasiliensis
B. Sporothrix schenckii
C. Coccidioides immitis
D. Histoplasma capsulatum
A. Paracoccidioides brasiliensis
P. brasiliensis yeast forms are sometimes seen as a “mariner’s wheel” because multiple budding cells completely surround the periphery of the parent cell.
Which of the following is a key characteristic ofCoccidioides immitis?
A. Has a higher dissemination rate in white females
B. Is endemic in the northeastern United States
C. Produces endosporulating spherules in tissue
D. Forms foot cells
C. Produces endosporulating spherules in tissue
Coccidioides immitis is endemic in hot, semi-arid climates such as the southwestern United States and northern Mexico. It is a saprobe in mold form (desert soil). It is the most virulent of all agents of human mycoses. Coccidioides causes mild infection in everyone who inhales it, but is usually asymptomatic and self-limiting. Dissemination in the immunocompromised population is much higher than found for other fungal agents. The part of its life cycle in the mammalian host is highlighted by the endosporulating spherules in tissue.
A 2-month-old infant in good health was scheduled for a checkup at the pediatrician’s office. After arriving for the appointment, the mother noted
white patches on the baby’s tongue and in his mouth. The baby constantly used a pacifier. What is the most likely organism causing the white patches?
A. Cryptococcus neoformans
B. Candida albicans
C. Aspergillus fumigatus
D. None of these options
B. Candida albicans
An India ink test was performed on CSF from an HIV-infected male patient. Many encapsulated yeast cells were seen in the centrifuged sample. Further testing revealed a positive urease test and growth of brown colonies on niger-seed agar. The diagnosis of meningitis was caused by which yeast?
A. Candida albicans
B. Cryptococcus neoformans
C. Cryptococcus laurentii
D. Candida tropicalis
B. Cryptococcus neoformans
Immunocompromised patients are at risk for invasion of Cryptococcus neoformans. The polysaccharide capsule of C. neoformans is not recognized by phagocytes, which allow patients with impaired cell-mediated immunity to become readily infected with C. neoformans.
Which of the following is a key characteristic by which an
unknownCryptococcusspp. can be identfied asCryptococcus
neoformans?
A. Appearance of yellow colonies
B. Positive urease test
C. Presence of a capsule
D. Positive niger seed agar test
D. Positive niger seed agar test
Cryptococcus neoformans can be differentiated from other Cryptococcus species through the use of the Niger seed test; C. neoformans is Niger seed–positive (dark colonies).
Classification of viruses is made by:
A. Complement fixation serology
B. Electron microscopy
C. Nucleic acid composition
D. Cellular inclusion bodies
C. Nucleic acid composition
True viruses have nucleic acid that is either RNA or DNA, and this serves as the basis for initial classification. Members of these classes are further divided into groups that cause human disease based upon the mode of transmission, tissues invaded, diseases produced, and antigenic characteristics.
Which virus is the most common etiological agent of viral respiratory diseases in infants and children?
A. Respiratory syncytial virus (RSV)
B. Measles virus
C. Coxsackie A virus
D. Coxsackie B virus
A. Respiratory syncytial virus (RSV)
RSV is the cause of croup, bronchitis, bronchiolitis, and interstitial pneumonia. Children under 1 year old who are hospitalized are the most susceptible group.
The most common viral syndrome of pericarditis, myocarditis, and
pleurodynia (pain upon breathing) is caused by:
A. Herpes simplex virus
B. Respiratory syncytial virus
C. Epstein–Barr virus
D. Coxsackie B virus
D. Coxsackie B virus
Coxsackie A virus, Coxsackie B virus, and the echoviruses are most commonly implicated in myocarditis and other syndromes, including acute cerebellar ataxia and hepatitis. Like poliovirus, infections are more common in the summer and fall and gain entry through the gastrointestinal tract.
Which of the following viruses is implicated along with Epstein–Barr virus as a cause of infectious mononucleosis?
A. Cytomegalovirus (CMV)
B. Coxsackie A virus
C. Coxsackie B virus
D. Hepatitis B virus
A. Cytomegalovirus (CMV)
CMV infection in a previously healthy individual causes a self-limited mononucleosis syndrome. CMV is an opportunistic pathogen that may produce lifelong infections and can cause a variety of diseases, including congenital and neonatal infection, hepatitis, pneumonia, and disseminated infection in immunocompromised patients.
Which virus belonging to the Reoviridae group causes gastroenteritis in infants and young children but an asymptomatic infection in adults?
A. Coxsackie B virus
B. Rotavirus
C. Respiratory syncytial virus
D. Rhabdovirus
B. Rotavirus
Rotaviruses have been implicated in both nosocomial infections and epidemic gastroenteritis. Children 3–24 months old are most commonly affected. Diarrhea begins after an incubation period of 3 days, lasts for 2–10 days, and is associated with vomiting and dehydration. In immunosuppressed children, rotavirus causes a chronic infection.
A very small, single-stranded DNA virus that causes a febrile illness with a rash and is called the fifth childhood disease after rubeola, rubella, varicella, and roseola is:
A. Rotavirus
B. Adenovirus type 40
C. Coxsackie A virus
D. Parvovirus B19
D. Parvovirus B19
Parvovirus causes a fever and characteristic “slapped cheek” rash in young children. Adults are usually immune, but immunocompromised persons may exhibit an arthritis or anemia (the virus infects immature RBCs in the bone marrow).
Hepatitis B virus can be transmitted by:
A. Acupuncture
B. Tattoos
C. Sexual contact
D. All of these options
D. All of these options
Which hepatitis B marker is the best indicator of early acute infection?
A. HBs Ag
B. HBe Ag
C. Anti-HBc
D. Anti-HBs
A. HBs Ag
Hepatitis B surface antigen (HBsAg) is the first marker to appear in hepatitis B virus infection. It is usually detected within 4 weeks of exposure (prior to the rise in transaminases) and persists for about 3 months after serum enzyme levels return to normal.
Which marker is a reliable marker for the presence of high levels of hepatitis B virus (HBV) and a high degree of infectivity?
A. HBe Ag
B. HBs Ag
C. HBc Ag
D. Anti-HBs
A. HBe Ag
Which is the first antibody detected in serum after infection with hepatitis B virus (HBV)?
A. Anti-HBs
B. Anti-HBc IgM
C. Anti-HBe
D. All are detectable at the same time
B. Anti-HBc IgM
Antibody to the hepatitis B core antigen (anti-HBc) is the first detectable hepatitis B antibody. It persists in the serum for 1–2 years postinfection and is found in the serum of asymptomatic carriers of HBV. Because levels of total anti-HBc are high after recovery, IgM anti-HBc is a more useful marker for acute infection. Both anti-HBc and anti-HBs can persist for life, but only anti-HBs is considered protective.
Which hepatitis antibody confers immunity against reinfection with
hepatitis B virus?
A. Anti-HBc IgM
B. Anti-HBc IgG
C. Anti-HBe
D. Anti-HBs
D. Anti-HBs
Anti-HBs appears later in infection than anti-HBc and is used as a marker for immunity following infection or vaccination rather than for diagnosis of current infection.
A young father of two small children complained of a rash on the torso of his body. The children had been diagnosed with chickenpox and confined
to their home. The father had experienced chickenpox as a child and knew he did not have the same rash as his children. What is the most likely cause of the father’s rash?
A. Herpes simplex 1 virus
B. Varicella-zoster virus
C. Herpes simplex 2 virus
D. Epstein–Barr virus
B. Varicella-zoster virus
Varicella-zoster virus is the cause of an infection with chickenpox. As an adult, the father is experiencing shingles, a reactivation of the virus. The virus lies dormant in the sensory (dorsal root) ganglia of the spinal nerves, and its reactivation produces a nonweeping blisterlike rash on an inflamed skin base that follows the path of the underlying nerves.
An immunocompromised patient was admittedto the hospital with a diagnosis of hemorrhagic cystitis. Which combination of virus and specimen would be most appropriate to diagnose a viral cause of this disorder?
A. BK virus—urine
B. Human papilloma virus—skin
C. Epstein–Barr virus—serum
D. Hepatitis B virus—serum
A. BK virus—urine
The BK virus, a polyoma virus, is transmitted by direct contact with infected respiratory secretions. It has tropism for the urinary system, and often causes a latent, asymptomatic infection in the kidney. However, in immunocompromised patients, the virus is often implicated in renal and bladder infections. Kidney failure caused by BK virus is a significant concern in bone marrow and renal transplant recipients.
The appearance of Koplik spots in the oral mucosa of patients is
characteristic of infection with what viral agent?
A. Hepatitis
B. Measles
C. Rabies
D. Smallpox
B. Measles
Koplik spots are diagnostic for measles infection and represent necrotic vesicles with a white center surrounded by erythema.
Kaposi sarcoma is associated with infection by:
A. Adenovirus
B. Cytomegalovirus
C. Hepatitis E vims
D. Human herpes virus 8
D. Human herpes virus 8
Kaposi sarcoma, a relatively common cancer in patients with AIDS, has been linked to human herpes virus 8.
Negri bodies may be found in brain tissue of humans or animals infected with:
A. Adenovirus
B. Filovirus
C. Measles virus
D. Rabies virus
D. Rabies virus
Rabies is a neurotropic virus that causes extensive destruction in the brain. Negri bodies are seen in the cytoplasm of large ganglion cells and are demonstrated by Seller’s stain. Rabies in humans or lower animals can be diagnosed by demonstration of these characteristic inclusions.
The virus associated with warts is:
A. Flavivirus
B. Morbillivirus
C. Mumps virus
D. Papillomavirus
D. Papillomavirus
The etiologic agents for the numerous benign cutaneous and mucosal lesions known as warts are the human papillomaviruses (HPVs).
A dehydrated 25-year-old male patient was admitted to the hospital with SYMPTOMS SIMILAR TO THOSE OF CHRONIC FATIGUE SYNDROME. Serological testing proved negative for recent streptococcal infection,
Epstein–Barr virus, and hepatitis. Which of the following viral serological tests should help with a possible diagnosis?
A. CMV
B. Echovirus
C. Respiratory syncytial virus
D. Measles virus
A. CMV
Collection of specimens from cutaneous vesicles for detection of these viruses may require a TZANCK SMEAR:
A. CMV and EBV
B. HSV and VZV
C. JC and BK polyomavirus
D. HBV and HCV
B. HSV and VZV
Transient aplastic crisis can occur with:
A. Parvovirus B19
B. West Nile virus
C. Cytomegalovirus
D. Epstein Barr virus
A. Parvovirus B19
The filovirus that has a characteristic “shepherd’s hook” morphology when viewed by electron microscopy is:
A. Ebola Zaire virus
B. Ebola Reston virus
C. Ebola Sudan virus
D. Marburg virus
D. Marburg virus
Slow but continuing replication of damaged virus in the brain gives rise to SUBACUTE SCLEROSING PANENCEPHALITIS:
A. Measles virus
B. Mumps virus
C. Parainfluenza virus
D. Respiratory syncytial virus (RSV)
A. Measles virus
Subacute sclerosing panencephalitis (defective measles virus infection of CNS).
Most common cause of ASEPTIC MENINGITIS, an inflammation of the brain parenchyma:
A. Arenavirus
B. Cytomegalovirus
C. Enterovirus
D. Herpes simplex virus 2
C. Enterovirus
A 3-year-old female was admitted to the hospital following a 2-day visit with relatives over the Christmas holidays. Vomiting and diarrhea left the child severely dehydrated. No other members of the family were affected.
All bacterial cultures proved negative. A stool sample should be tested for which virus?
Adenovirus
CMV
Hepatitis D
Rotavirus
Rotavirus
Which of the following viruses is implicated along with Epstein–Barr virus as a cause of infectious mononucleosis?
A. Cytomegalovirus (CMV)
B. Coxsackie A virus
C. Coxsackie B virus
D. Hepatitis B virus
A. Cytomegalovirus (CMV)
CMV infection in a previously healthy individual causes a self-limited mononucleosis syndrome.
A very small, single-stranded DNA virus that causes a febrile illness with a rash and is called the fifth childhood disease after rubeola, rubella, varicella, and roseola is:
A. Rotavirus
B. Adenovirus type 40
C. Coxsackie A virus
D. Parvovirus B19
D. Parvovirus B19
Parvovirus causes a fever and characteristic “slapped cheek” rash in young children. Adults are usually immune, but immunocompromised persons may exhibit an arthritis or anemia (the virus infects immature RBCs in the bone marrow).
Which of the following viruses are thought to predominately cause gastroenteritis?
A. Hepadnaviruses
B. Filoviruses
C. Noroviruses
D. Arboviruses
C. Noroviruses
Norovirus is an important cause of gastroenteritis in several settings, including closed environments such as cruise ships and long-term care facilities. None of the other viruses listed are associated with gastroenteritis as a major symptom.
Which of the following groups contains the SARS virus?
A. Calicivirus
B. Coronavirus
C. Flavivirus
D. Filovirus
B. Coronavirus
The severe acute respiratory syndrome (SARS) virus arose as a previously unrecognized organism causing serious respiratory tract infections. This virus has been shown to be part of the coronavirus group.
Which of the following groups of virus is best described as:
- ssRNA, enveloped
- Pleomorphic/spherical capsid
- Large club-shaped spikes on surface gives “corona”effect
- Causes approximately 15% of coldlike illness
A. Influenza A
B. Influenza B
C. Coronaviruses
D. Pneumovirus
C. Coronaviruses
This is the description of the coronavirus group.
Which of the following is the specimen of choice for detecting rotavirus?
A. Throat swab
B. Urine sample
C. Bronchoalveolar wash
D. Feces sample
D. Feces sample
Rotaviruses are responsible for significant out- breaks of gastroenteritis and are an enteric virus. The specimen of choice for detecting this virus is stool.
The test of choice and most sensitive assay for use with CSF to diagnose aseptic meningitis caused by enterovirus is which of the following?
A. Cell culture
B. PCR
C. Antigenemia immunoassay
D. Shell vial assay
B. PCR
Nucleic amplification assays such as polymerase chain reaction are the most sensitive method for the detection of many/most viruses and patient samples, including cerebrospinal fluid for the diagnosis of meningitis.
A suspension of the test organism for use in broth dilution and disk diffusion testing is adjusted to match the turbidity of a:
A. #0.5 McFarland standard
B. #1.0 McFarland standard
C. #2.0 McFarland standard
D. #3.0 McFarland standard
A. #0.5 McFarland standard
McFarland turbidity standard is prepared by mixing ________ to obtain a solution with a specific optical density.
A. 1% hydrochloric acid and 1.175% barium chloride
B. 2% hydrochoric acid and 2.175% barium chloride
C. 1% sulfuric acid and 1.175% barium chloride
D. 2% sulfuric acid and 2.175% barium chloride
C. 1% sulfuric acid and 1.175% barium chloride
Seventy (70) percent recirculated to the cabinet work area through HEPA; 30% balance can be exhausted through HEPA back into the room or to outside through a canopy unit:
A. BSC Class I
B. BSC Class II, A1
C. BSC Class II, B1
D. BSC Class II, B2
B. BSC Class II, A1
Thirty (30) percent recirculated, 70% exhausted. Exhaust cabinet air must pass through a dedicated duct to the outside through a HEPA filter.
A. BSC Class I
B. BSC Class II, A1
C. BSC Class II, B1
D. BSC Class II, B2
C. BSC Class II, B1
No recirculation; total exhaust to the outside through a HEPA filter.
A. BSC Class I
B. BSC Class II, A1
C. BSC Class II, B1
D. BSC Class II, B2
D. BSC Class II, B2
Most effective at reducing hazards:
A. PPE
B. Administrative controls
C. Engineering controls
D. Substitution
E. Elimination
E. Elimination
In thioglycolate broth, strictly aerobic organisms:
Grow throughout the broth
Grow toward the top of the broth
Grow in the bottom of the broth
Demonstrate flocculation
Grow toward the top of the broth
In thioglycollate broth, these organisms will grow slightly below the surface
where oxygen concentrations are lower than atmospheric concentrations:
Obligate aerobes
Obligate anaerobes
Facultative anaerobes
Microareophilic organisms
Microareophilic organisms
An isolate of Staphylococcus aureus was cultured from an ulcer obtained from
the leg of a diabetic 79-year-old female patient. The organism showed
resistance to methicillin. Additionally, this isolate should be tested for
resistance or susceptibility to:
Erythromycin
Gentamicin
Vancomycin
Kanamycin
Vancomycin
Resistance to clindamycin can be induced in vitro by:
Ampicillin
Erythromycin
Gentamicin
Penicillin
Erythromycin
Greater than 100,000 CFU/mL of a gram-negative bacilli were isolated on
MacConkey from a urine specimen. Biochemical results are as follows:
Glucose: acid, gas produced; Indole: negative; urea: positive; H2S: positive.
The organism is most likely:
Morganella morganii
Proteus vulgaris
Proteus mirabilis
Providencia stuartii
Proteus mirabilis
Flocked swab:
Cotton
Gauze
Cotton and gauze
Nylon
Nylon
NYLON STRANDS ARE SPRAYED OR FLOCKED ONTO THE TIP.
The steam autoclave method of sterilization:
Uses 15 lbs of pressure for 15 minutes
Utilizes dry heat for 20 minutes
Produces a maximum temperature of 100ºC
Requires a source of ethylene oxide
Uses 15 lbs of pressure for 15 minutes
he traditional gravity displacement of steam sterilization cycle is 121˚C for 15 minutes at 15 pounds per square inch. Ethylene dioxide is an alternative sterilization method.
