BACTE Flashcards
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
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 most important diagnostic tool in treating patients with clinical infections in the emergency department:
AFB stain
Culture
Gram stain
IMVic reaction
Gram stain
Additional tests to be included with the IMViC reaction:
Bacitracin and SXT susceptibility
Catalase and coagulase
Motility and H2S
Oxidase and urease
Motility and H2S
These 4 IMViC tests (actually 6 tests if you include motility and H2S) constitute, perhaps, the most critical tests used for identification of bacteria after the gram stain. The test results from these 6 tests should carry more weight than almost any other tests, certainly higher priority than sugar results since they are more stable reactions.
Salmonella Shigella (SS) Agar is a modification of:
BAP
CAP
DCA
EMB
DCA
Salmonella Shigella (SS) Agar is a modification of the Deoxycholate Citrate Agar.
Cary-Blair indicator changes from red to yellow color:
Buffering capacity was overcomed
Change in the pH of the medium
Low temperature
Presence of contaminants
Buffering capacity was overcomed
Some stool specimens may be highly acidic and will overcome the buffering capacity of the medium. This will cause the red indicator to shift to a yellow color. Discard the medium if it has turned yellow and request another specimen.
When cultured in thioglycollate broth, these organisms grow slightly below the surface where oxygen concentrations are lower than atmospheric concentrations
Aerotolerant anaerobes
Facultative anaerobes
Microaerophilic organisms
Obligate aerobes
Microaerophilic organisms
In addition to amount of growth present, the location of growth within thioglycollate broth indicates the type of organism present based on oxygen requirements.
Strict anaerobes will grow at the bottom of the broth tube, whereas aerobes will grow near the surface.
Microaerophilic organisms will grow slightly below the surface where oxygen concentrations are lower than atmospheric concentrations.
In addition, facultative anaerobes and aerotolerant organisms will grow throughout the medium, as they are unaffected by the variation in oxygen content.
Which one of the following specimen requests is acceptable?
Feces submitted for anaerobic culture
Foley catheter tip submitted for aerobic culture
Rectal swab submitted for direct smear for gonococci
Urine for culture of acid-fast bacilli
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.
Which of the following is the most appropriate method for collecting a urine specimen from a patient with an indwelling catheter?
Remove the catheter, cut the tip, and submit it for culture
Disconnect the catheter from the bag, and collect urine from the terminal end of the catheter
Collect urine directly from the bag
Aspirate urine aseptically from the catheter tubing
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).
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:
Examined for the presence of Entamoeba hartmanni
Examined for the presence of Camylobacter sp
Screened for the detection of enterotoxigenic Escherichia coli
Placed in thioglycollate broth to detect Clostridium
botulinum
Examined for the presence of Camylobacter 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.
Composition of 0.5 McFarland standard:
1% sulfuric acid and 2.175% barium chloride
1% sulfuric acid and 1.175% barium chloride
1% hydrochloric acid and 2.175% barium chloride
1% hydrochloric acid and 1.175% barium chloride
1% sulfuric acid and 1.175% barium chloride
0.5 McFarland (barium sulfate) standard:
1% sulfuric acid
1.175% barium chloride
Standard agar depth of the Mueller-Hinton agar:
1 to 2 mm
3 to 5 mm
6 to 8 mm
7 to 9 mm
3 to 5 mm
MUELLER-HINTON AGAR
STANDARD AGAR DEPTH
3 to 5 mm. (average of 4 mm.)
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?
The antibiotic disks were not stored with the proper desiccant
The depth of the media was too thick
The depth of the media was too thin
The antibiotic disks were not properly applied to the media
The depth of the media was too thin
Quality control results for disk diffusion susceptibility tests yield the following results: aminoglycoside zones too small and penicillin zones too large. This is most likely due to the:
Inoculum being too heavy
Inoculum being too light
pH of Mueller-Hinton agar being too low
Calcium and magnesium concentration in the agar being too high
pH of Mueller-Hinton agar being too low
Mueller-Hinton Agar used for disk diffusion is standardized at pH 7.2 to 7.4. Penicillin function better in an acidic environment, so zone sizes would become larger if the media pH is too low. Aminoglycosides, on the other hand are less effective in an acidic environment, so zone sizes would become smaller if the pH of the media is too low.
In disk diffusion susceptibility testing, as an antimicrobial agent diffuses away from the disk, the concentration of antibiotic is:
Increased
Decreased
Unchanged
Inoculum dependent
Decreased
As it diffuses into the media, the concentration of antibiotic gets lower the further it diffuses from the disk.
After satisfactory performance of daily disk diffusion susceptibility quality control is documented, the frequency of quality control can be reduced to:
Twice a week
Every week
Every other week
Every month
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.
An outbreak of Staphylococcus aureus has occurred in a hospital nursery. In order to establish the epidemiological source of the outbreak, the most commonly used typing method is:
Pulsed-field gel electrophoresis
Serological typing
Coagulase testing
Catalase testing
Pulsed-field gel electrophoresis
The most commonly used method to determine the relatedness of 2 or more bacterial strains is pulsed-field gel electrophoresis.
The organism most commonly associated with neonatal purulent meningitis is:
N. meningitidis
S. pneumoniae
S. agalactiae
S. pyogenes
S. agalactiae
All of the organisms listed are potential causes of meningitis. Group B streptococcus is also associated with neonatal meningitis and meningitis of the elderly.
One of the enterotoxins produced by enterotoxigenic Escherichia coli in traveler’s diarrhea is similar to a toxin produced by:
Clostridium perfringens
Clostridium difficile
Vibrio cholerae
Yersinia enterocolitica
Vibrio cholerae
The toxin produced by enterotoxigenic E. coli is similar in action and amino acid sequence to cholera toxin.
Which of the following sets of tests best differentiates Salmonella and Citrobacter species?
KCN, malonate, beta-galactosidase, lysine decarboxylase
Dulcitol, citrate, indole, H2S production
Lactose, adonitol, KCN, motility
Lysine decarboxylase, lactose, sucrose, malonate, indole
KCN, malonate, beta-galactosidase, lysine decarboxylase
Salmonella are positive for lysine decarboxylase and most are negative for KCN, malonate and ONPG. Citrobacter are negative for lysine decarboxylase and positive for growth in KCN.
The Oriental rat flea, Xenopsylla cheopis, can be involved in transmitting which of the following microorganisms?
Bartonella quintana
Plasmodium spp.
Rickettsia prowazeki
Yersinia pestis
Yersinia pestis
Oxidase positive, urease negative:
Bordetella bronchiseptica
Bordetella pertussis
Bordetella parapertussis
All of these
Bordetella pertussis
A culture from an infected dog bite on a small boy’s finger yielded a small, gram-negative coccobacillus that was smooth, raised and beta-hemolytic on blood agar. The isolate grew on MacConkey agar, forming colorless colonies. The organism was motile, catalase positive, oxidase positive, reduced nitrate, and was urease positive within 4 hours. No carbohydrates were fermented. The most likely identification of this isolate is:
Brucella canis
Yersinia pestis
Francisella tularensis
Bordetella bronchiseptica
Bordetella bronchiseptica
Bordetella bronchiseptica are normal flora in the respiratory tract of various animals. A key reaction is that it is rapidly urea positive (within 4 hours). Brucella is also urea positive, but does not grow in MacConkey agar.
While swimming in a lake near his home, a young boy cut his foot, and an infection developed. The culture grew a nonfastidious gram-negative, oxidase positive, beta hemolytic, motile bacilli that produced deoxyribonuclease. The most likely identification is:
Enterobacter cloacae
Serratia marcescens
Aeromonas hydrophila
Escherichia coli
Aeromonas hydrophila
Enterobacteriaceae, such as E. coli, Serratia and Enterobacter are oxidase negative. The only selection that is oxidase positive is Aeromonas. It is associated with wounds contaminated with water.
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:
Colistin nalidixic acid for Listeria
MacConkey agar with sorbitol for Campylobacter
Mannitol salt agar for Enterococcus species
Thiosulfate citrate bile salts sucrose for Vibrio species
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.
Stool specimens suspected of containing Vibrio spp. should be collected and transported only in:
Amies medium
Cary-Blair medium
Stuart’s medium
Transgrow medium
Cary-Blair medium
Stool specimens suspected of containing Vibrio spp. should be collected and transported only in Cary-Blair medium.
Catalase positive, lactose negative, xylose positive:
Haemophilus aegypticus
Haemophilus ducreyi
Haemophilus parainfluenzae
Haemophilus influenzae
Haemophilus influenzae
The best procedure to differentiate Listeria monocytogenes from Corynebacterium species is:
Catalase
Motility at 25C
Motility at 35C
Gram stain
Motility at 25C
Corynebacterium and Listeria are catalase positive and gram positive bacilli. Listeria demonstrate “tumbling motility” that is best demonstrated following growth at 25˚C. A few species of Corynebacterium are motile when grown at 35˚C.
A patient has a suspected diagnosis of subacute bacterial endocarditis. His blood cultures grow non-spore-forming pleomorphic gram-positive bacilli only in the anaerobic bottle. What test(s) will give a presumptive identification of this microorganism?
Beta-hemolysis and oxidase
Catalase and spot indole
Esculin hydrolysis
Gelatin hydrolysis
Catalase and spot indole
Propionibacterium acnes is part of the normal flora on the skin and is a common blood culture contaminant. The gram stain given is typical for P. acnes, and it is catalase and indole positive.
Colonies appear shiny and mucoid because of the presence of a polysaccharide capsule:
Candida albicans
Cryptococcus neoformans
Malassezia furfur
Histoplasma capsulatum
Cryptococcus neoformans
LATEX AGGLUTINATION for cryptococcal _____ is now recommended test for Cryptococcus neoformans.
Polysaccharide capsule
Antigen
Antibody
Nucleic acids
Antigen
A mold grown at 25C exhibited delicate septate hyaline hyphae and many conidiophores extending at right angles from the hyphae. Oval, 2-5 um conidia were formed at the end of the conidiophores giving a flowerlike appearance. In some areas “sleeves” of spores could be found along the hyphae as well. A 37C culture of this organism produced small, cigar-shaped yeast cells. This organism is most likely:
Histoplasma capsulatum
Sporothrix schenckii
Blastomyces dermatitidis
Coccidioides immitis
Sporothrix schenckii
Virulence factors include aflatoxin, serine protease and aspartic acid proteinase:
Aspergillus spp.
Blastomyces dermatitidis
Cryptococcus neoformans
Histoplasma capsulatum
Aspergillus spp.
Most often, ______ are “dead-end” hosts.
Amphibians
Birds
Humans
Rodents
Humans
Most often, humans are “dead-end” hosts, meaning that there is no subsequent human-to-human transmission.
Delay in the processing of fluid specimens requires dilution in a viral transport medium before storage:
1: 2 to 1:5
1:10 to 1:20
1:50 to 1:100
1:100 to 1:200
1: 2 to 1:5
The most sensitive method for the detection of β-lactamase in bacteria is by the use of:
Chromogenic cephalosporin
Penicillin
Oxidase
Chloramphenicol acetyltransferase
Chromogenic cephalosporin
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 Proteus species?
The swarming area should be ignored
The results of the disk diffusion method are invalid
The swarming area should be measured as the growth boundary
The isolate should be retested after diluting to a 0.05 McFarland standard
The swarming area should be ignored
Antimicrobial susceptibility testing of anaerobes is done by which of the following methods?
Broth disk elution
Disk agar diffusion
Microtube broth dilution
β-Lactamase testing
Microtube broth dilution
The anaerobes are not suited for the broth disk elution or disk agar diffusion tests because of their slow rate of growth. Kirby–Bauer method reference charts are not designed to be used as a reference of susceptibility for anaerobes.
Cerebrospinal fluid (CSF) should be cultured immediately, but if delayed the specimen should be:
Refrigerated at 4°C to 6°C
Frozen at –20°C
Stored at room temperature for no longer than 24 hours
Incubated at 37°C and cultured as soon as possible
Incubated at 37°C and cultured as soon as possible
Select the method of choice for recovery of anaerobic bacteria from a deep abscess.
Cotton fiber swab of the abscess area
Skin snip of the surface tissue
Needle aspirate after surface decontamination
Swab of the scalpel used for débridement
Needle aspirate after surface decontamination
Anaerobic bacteria are routinely isolated from all of the following types of infections except:
Lung abscesses
Brain abscesses
Dental infections
Urinary tract infections
Urinary tract infections
The incidence of anaerobic bacteria recovered from the urine is approximately 1% of isolates. The other three types of infection are associated with a 60%–93% incidence of anaerobic recovery. Urine is not cultured routinely under anaerobic conditions unless obtained surgically (e.g., suprapubic aspiration).
Prereduced and vitamin K1-supplemented blood agar plates are recommended isolation media for:
Mycobacterium marinum and Mycobacterium avium intracellulare
Bacteroides, Peptostreptococcus, and Clostridium spp.
Proteus spp.
Enterococcus spp.
Bacteroides, Peptostreptococcus, and Clostridium spp.
Anaerobic culture media can be prereduced before sterilization by boiling, saturation with oxygen-free gas, and addition of cysteine or other thiol compounds. The final oxidation reduction potential (Eh) of the medium should be approximately –150 mV to minimize the effects of exposure of organisms to oxygen during inoculation.
Which of the following is the medium of choice for the selective recovery of gram-negative anaerobes?
Kanamycin–vancomycin (KV) agar
Phenylethyl alcohol (PEA) agar
Cycloserine–cefoxitin–fructose agar (CCFA)
THIO broth
Kanamycin–vancomycin (KV) agar
Methods other than packaged microsystems used to identify anaerobes include:
Antimicrobial susceptibility testing
Gas–liquid chromatography (GLC)
Special staining
Enzyme immunoassay
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.
Semisolid transport media such as Amies, Stuart, or Cary–Blair are suitable for the transport of swabs for culture of most pathogens except:
Neisseria gonorrhoeae
Enterobacteriaceae
Campylobacter fetus
Streptococcus pneumoniae
Neisseria gonorrhoeae
Colistin–nalidixic acid agar (CNA) is used primarily for the recovery of:
Neisseria species
Enterobacteriaceae
Pseudomonas aeruginosa
Staphylococcus aureus
Staphylococcus aureus
Toxic shock syndrome is attributed to infection with:
Staphylococcus epidermidis
Staphylococcus hominis
Staphylococcus aureus
Staphylococcus saprophyticus
Staphylococcus aureus
Which Staphylococcus species, in addition to S. aureus, also produces coagulase?
S. intermedius
S. saprophyticus
S. hominis
All of these options
S. intermedius
An isolate of Staphylococcus aureus was cultured from an ulcer obtained from the leg of a diabetic79-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
MRSA isolates are usually tested for susceptibility or resistance to vancomycin, a glycopeptide.
Resistance to which drug categorizes a strain of Staphylococcus aureus as methicillin-resistant Staphylococcus aureus (MRSA)?
Oxacillin
Colistin
Trimethoprim–sulfamethoxazole
Tetracycline
Oxacillin
Oxacillin is the drug used to screen staphylococci for resistance to antibiotics having the β-lactam ring. Included in this group are penicillin, cephalosporin, monobactam, and carbapenem.
MRSA defines strains of staph that are resistant to all of these antibiotic groups. MRSA strains are treated with vancomycin or oxazolidinone.
Which test is used for the determination of inducible clindamycin resistance in staphylococci and streptococci?
E-test
D-zone test
A-test
CAMP test
D-zone test
An outbreak of Staphylococcus aureus in the nursery department prompted the Infection Control Committee to proceed with an environmental screening procedure. The best screening media to use for this purpose would be:
CNA agar
THIO broth
Mannitol salt agar
PEA agar
Mannitol salt agar
Streptococcus species exhibit which of the following properties?
Aerobic, oxidase positive, and catalase positive
Facultative anaerobe, oxidase negative, catalase negative
Facultative anaerobe, β-hemolytic, catalase positive
May be α-, β-, or γ-hemolytic, catalase positive
Facultative anaerobe, oxidase negative, catalase negative
An isolate recovered from a vaginal culture obtained from a 25-year-old female patient who is 8 months pregnant is shown to be a gram-positive cocci, catalase negative, and β-hemolytic on blood agar. Which tests are needed for further identification?
Optochin, bile solubility, PYR
Bacitracin, CAMP, PYR
Methicillin, PYR, trehalose
Coagulase, glucose, PYR
Bacitracin, CAMP, PYR
Group B streptococci (S. agalactiae) are important pathogens and can cause serious neonatal infections. Women who are found to be heavily colonized vaginally with S. agalactiae pose a threat to the newborn, especially within the first few days after delivery. The infection acquired by the infant is associated with pneumonia.
The bile solubility test causes the lysis of:
Streptococcus bovis colonies on a blood agar plate
Streptococcus pneumoniae colonies on a blood agar plate
Group A streptococci in broth culture
Group B streptococci in broth culture
Streptococcus pneumoniae colonies on a blood agar plate
Nutritionally variant streptococci (NVS) require specific thiol compounds, cysteine, or the active form of vitamin B6. Which of the following tests supplies these requirements?
CAMP test
Bacitracin susceptibility test
Bile solubility test
Staphylococcal cross-streak test
Staphylococcal cross-streak test
All of the following are appropriate when attempting to isolate N. gonorrhoeae from a genital specimen except:
Transport the genital swab in charcoal transport medium
Plate the specimen on modified Thayer–Martin (MTM) medium
Plate the specimen on New York City or Martin-Lewis agar
Culture specimens in ambient oxygen at 37°C
Culture specimens in ambient oxygen at 37°C
Cultures must be incubated in 3%–7% CO2 at 35°C.
A Gram stain of a urethral discharge from a man showing extracellular and intracellular gram-negative diplococci within segmented neutrophils is a presumptive identification for:
Neisseria gonorrhoeae
Neisseria meningitidis
Moraxella (Branhamella) catarrhalis
Neisseria lactamica
Neisseria gonorrhoeae
The β-galactosidase test aids in the identification of which Neisseria species?
N. lactamica
N. meningitidis
N. gonorrhoeae
N. flavescens
N. lactamica
Deoxycholate agar (DCA) is useful for the isolation of:
Enterobacteriaceae
Enterococcus spp.
Staphylococcus spp.
Neisseria spp.
Enterobacteriaceae
Xylose lysine deoxycholate (XLD) agar is a highly selective medium used for the recovery of which bacteria?
Staphylococcus spp. from normal flora
Yersinia spp. that do not grow on Hektoen agar
Enterobacteriaceae from gastrointestinal specimens
Streptococcus spp. from stool cultures
Enterobacteriaceae from gastrointestinal specimens
The Voges–Proskauer (VP) test detects which end product of glucose fermentation?
Acetoin
Nitrite
Acetic acid
Hydrogen sulfide
Acetoin
At which pH does the methyl red (MR) test become positive?
7.0
6.5
6.0
4.5
4.5
The ortho-nitrophenyl-β-galactopyranoside(ONPG) test is most useful when differentiating:
Salmonella spp. from Pseudomonas spp.
Shigella spp. from some strains of Escherichia coli
Klebsiella spp. from Enterobacter spp.
Proteus vulgaris from Salmonella spp.
Shigella spp. from some strains of Escherichia coli
In the test for urease production, ammonia reacts to form which product?
Ammonium citrate
Ammonium carbonate
Ammonium oxalate
Ammonium nitrate
Ammonium carbonate
The test for urease production is based on the ability of the colonies to hydrolyze urea in Stuart broth or Christensen agar to form CO2 and ammonia. These products form ammonium carbonate, resulting in alkalinization. This turns the pH indicator (phenol red) pink at pH 8.0.
Which of the following reagents is added to detect the production of indole?
p-Dimethylaminobenzaldehyde
Bromcresol purple
Methyl red
Cytochrome oxidase
p-Dimethylaminobenzaldehyde
Decarboxylation of the amino acids lysine, ornithine, and arginine results in the formation of:
Ammonia
Urea
CO2
Amines
Amines
Putrescine is an alkaline amine product of which bacterial enzyme?
Arginine decarboxylase
Phenylalanine deaminase
Ornithine decarboxylase
Lysine decarboxylase
Ornithine decarboxylase
Which genera are positive for phenylalanine deaminase
Enterobacter, Escherichia, and Salmonella
Morganella, Providencia, and Proteus
Klebsiella and Enterobacter
Proteus, Escherichia, and Shigella
Morganella, Providencia, and Proteus
Biochemically, the Enterobacteriaceae are gram-negative rods that:
Ferment glucose, reduce nitrate to nitrite, and are oxidase negative
Ferment glucose, produce indophenol oxidase, and form gas
Ferment lactose and reduce nitrite to nitrogen gas
Ferment lactose and produce indophenol oxidase
Ferment glucose, reduce nitrate to nitrite, and are oxidase negative
Care must be taken when identifying biochemical isolates of Shigella because serological cross-reactions occur with:
E. coli
Salmonella spp.
Pseudomonas spp.
Proteus spp.
E. coli
Which of the following tests best differentiates Shigella species from E. coli?
Hydrogen sulfide, VP, citrate, and urease
Lactose, indole, ONPG, and motility
Hydrogen sulfide, MR, citrate, and urease
Gas, citrate, and VP
Lactose, indole, ONPG, and motility
E. coli, positive for lactose, indole, and ONPG are usually motile. Shigella species do not ferment lactose or produce indole, lack β-galactosidase, and are nonmotile.
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:
Campylobacter spp.
Salmonella spp.
Proteus spp.
Yersinia spp.
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 gram-negative rod is recovered from a catheterized urine sample from a nursing home patient. The lactose-negative isolate tested positive for indole, urease, ornithine decarboxylase, and phenylalanine deaminase and negative for H2S.The most probable identification is:
Edwardsiella spp.
Morganella spp.
Ewingella spp.
Shigella spp.
Morganella spp.
The Shiga-like toxin (verotoxin) is produced mainly by which Enterobacteriaceae?
Klebsiella pneumoniae
E. coli
Salmonella typhimurium
Enterobacter cloacae
E. coli
Following a 2-week camping trip to the Southwest (US), a 65-year-old male patient was hospitalized with a high fever and an inflammatory swelling of the axilla and groin lymph nodes. Several blood cultures were obtained, resulting in growth of gram-negative rods resembling “closed safety pins.” The organism grew on MacConkey’s agar showing non–lactose-fermenting colonies. Testing demonstrated a nonmotile rod that was biochemically inert. What is the most likely identification?
Yersinia pestis
Klebsiella pneumoniae
Proteus vulgaris
Morganella morganii
Yersinia pestis
The majority of clinical laboratories with a microbiology department should have the capability of serotyping which pathogenic Enterobacteriaceae?
Yersinia enterocolitica, Shigella spp.
E. coli O157:H7, Salmonella spp., Shigella spp.
Yersinia pestis, Salmonella spp.
Edwardsiella spp., Salmonella spp.
E. coli O157:H7, Salmonella spp., Shigella spp.
The drugs of choice for treatment of infections with Enterobacteriaceae are:
Aminoglycosides, trimethoprim–sulfamethoxazole, third-generation cephalosporins
Ampicillin and nalidixic acid
Streptomycin and isoniazid
Chloramphenicol, ampicillin, and colistin
Aminoglycosides, trimethoprim–sulfamethoxazole, third-generation cephalosporins
Which isolates of the Enterobacteriaceae family most commonly produce extended-spectrumβ-lactamase (ESBL)?
E. coli and Klebsiella pneumoniae
Yersinia enterocolitica and Yersinia pestis
Morganella morganii and Proteus vulgaris
Salmonella typhi and Shigella sonnei
E. coli and Klebsiella pneumoniae
Which test group best differentiates Acinetobacter baumannii from P. aeruginosa?
Oxidase, motility, NO3 reduction
MacConkey growth, 37°C growth, catalase
Blood agar growth, oxidase, catalase
Oxidase, TSI, MacConkey growth
Oxidase, motility, NO3 reduction
Acinetobacter spp. are nonmotile rods that appear as coccobacillary forms from clinical specimens. All are oxidase negative and catalase positive. P. aeruginosa reduces NO3 to NO2, while A. baumannii does not.
Which organism is associated with immunodeficiency syndromes and melioidosis (a glanders-like disease in Southeast Asia and northern Australia)?
Pseudomonas aeruginosa
Pseudomonas stutzeri
Pseudomonas putida
Burkholderia pseudomallei
Burkholderia pseudomallei
Which biochemical tests are needed to differentiate Burkholderia cepacia from S. maltophilia?
Pigment on blood agar, oxidase, DNase
Pigment on MacConkey agar, flagellar stain, motility
Glucose, maltose, lysine decarboxylase
TSI, motility, oxidase
Pigment on blood agar, oxidase, DNase
Both organisms produce yellowish pigment and have polar tuft flagella, but the oxidase and DNase tests are differential.
Alcaligenes faecalis (formerly A. odorans) is distinguished from Bordetella bronchiseptica with which test?
Urease (rapid)
Oxidase
Growth on MacConkey agar
Motility
Urease (rapid)
Alcaligenes and Bordetella are genera belonging to the Alcaligenaceae family. The two organisms are very similar biochemically, but B. bronchiseptica is urease positive. Both organisms are oxidase positive, grow on MacConkey agar, and are motile by peritrichous flagella. B. bronchiseptica grows well on MacConkey agar but other species of Bordetella are fastidious gram-negative rods.
Alcaligenes faecalis (formerly A. odorans) is distinguished from Bordetella bronchiseptica with which test?
Urease (rapid)
Oxidase
Growth on MacConkey agar
Motility
Urease (rapid)
Alcaligenes and Bordetella are genera belonging to the Alcaligenaceae family. The two organisms are very similar biochemically, but B. bronchiseptica is urease positive. Both organisms are oxidase positive, grow on MacConkey agar, and are motile by peritrichous flagella. B. bronchiseptica grows well on MacConkey agar but other species of Bordetella are fastidious gram-negative rods.
Cetrimide agar is used as a selective isolation agar for which organism?
Acinetobacter spp.
Pseudomonas aeruginosa
Moraxella spp.
Stenotrophomonas maltophilia
Pseudomonas aeruginosa
Cetrimide agar is used as a selective isolation agar for which organism?
Acinetobacter spp.
Pseudomonas aeruginosa
Moraxella spp.
Stenotrophomonas maltophilia
Pseudomonas aeruginosa
Which of the listed Pseudomonas spp. is associated with the following virulence factors: exotoxin A, endotoxins, proteolytic enzymes, antimicrobial resistance, and production of alginate?
P. fluorescens
P. putida
P. stutzeri
P. aeruginosa
P. aeruginosa
Which of the listed Pseudomonas spp. is associated with the following virulence factors: exotoxin A, endotoxins, proteolytic enzymes, antimicrobial resistance, and production of alginate?
P. fluorescens
P. putida
P. stutzeri
P. aeruginosa
P. aeruginosa
Which of the listed Pseudomonas spp. is associated with the following virulence factors: exotoxin A, endotoxins, proteolytic enzymes, antimicrobial resistance, and production of alginate?
P. fluorescens
P. putida
P. stutzeri
P. aeruginosa
P. aeruginosa
Select the media of choice for recovery of Vibrio cholerae from a stool specimen.
MacConkey agar and thioglycollate media
Thiosulfate–citrate–bile–sucrose (TCBS) agar and alkaline peptone water (APW) broth
Blood agar and selenite-F (SEL) broth
CNA agar
Thiosulfate–citrate–bile–sucrose (TCBS) agar and alkaline peptone water (APW) broth
Abdominal pain, fever, vomiting, and nausea prompted an elderly male to seek medical attention. A watery stool specimen producing no fecal leukocytes or erythrocytes was cultured and grew a predominance of gram-negative fermentative bacilli. The colonies were beta-hemolytic on blood agar and cream colored on MacConkey agar. The colonies were both oxidase and catalase positive. What is the most likely identification?
Aeromonas hydrophilia
Escherichia coli
Salmonella spp.
Shigella spp.
Aeromonas hydrophilia
The oxidase positive test result rules out the members of the Enterobacteriaceae family.
Several attendees of a medical conference in the Gulf coast area became ill after frequenting a seafood restaurant. A presumptive identification of Vibrio cholera was made after stool specimens from several subjects grew clear colonies on MacConkey agar and yellow colonies on TCBS agar. Which key tests would help eliminate Aeromonas and Plesiomonas spp.?
Mannitol fermentation, Na+ requirement
Oxidase, motility
Oxidase, nitrate
Hemolysis on blood agar, catalase
Mannitol fermentation, Na+ requirement
All three organisms are positive for oxidase production and are motile. Plesiomonas spp. do not grow on TCBS agar. Clear colonies on MacConkey agar and yellow colonies on TCBS agar indicate Vibrio or Aeromonas spp. However, only Vibrio spp. require Na+ (1% NaCl) in the medium for growth.
Which of the following tests should be done first in order to differentiate Aeromonas spp. from the Enterobacteriaceae?
Urease
OF glucose
Oxidase
Catalase
Oxidase
Aeromonas growing on enteric media are differentiated from the Enterobacteriaceae by demonstrating that colonies are oxidase positive.
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?
5% O2, 10% CO2, and 85% N2
20% O2, 10% CO2, and 70% N2
20% O2, 20% CO2, and 60% N2
20% O2, 5% CO2, and 75% N2
5% O2, 10% CO2, and 85% N2
Which group of tests best differentiates Helicobacter pylori from C. jejuni?
Catalase, oxidase, and Gram stain
Catalase, oxidase, and nalidixic acid sensitivity
Catalase, oxidase, and cephalothin sensitivity
Urease, nitrate, and hippurate hydrolysis
Urease, nitrate, 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:
Capnocytophaga spp.
Pasteurella spp.
Proteus spp.
Pseudomonas spp
Pasteurella spp.
A 29-year-old male who often hunted rabbits and spent a lot of time in the woods was admitted to the hospital with skin ulcers on his upper extremities. At 48 hours, a small coccobacillus was recovered from the aerobic blood culture bottle only. The organism stained poorly with Gram stain, but did stain with acridine orange. Cultures taken from the ulcers did not grow on primary media. What is the most likely identification?
Pseudomonas aeruginosa
Pseudomonas fluorescens
Chryseobacterium spp.
Francisella tularensis
Francisella tularensis
An elderly woman who cared for several domestic cats was hospitalized with suspected cat-scratch disease (CSD). Blood cultures appeared negative, but a small, slightly curved pleomorphic gram-negative bacillus grew on BHI agar (brain, heart infusion agar with 5% horse or rabbit blood). What is the most likely identification?
Bartonella spp.
Brucella spp.
Kingella spp.
Haemophilus spp
Bartonella spp.
A neonate was readmitted to the hospital with a diagnosis of meningitis. The CSF revealed gram-negative straight rods. At 24 hours, the organism grew on 5% sheep blood and chocolate agars displaying a yellow pigment. On MacConkey agar, it appeared as a non–lactose fermenter. Colonies were oxidase, DNase, and gelatinase positive, and oxidized glucose and mannitol. What is the most likely identification?
Haemophilus influenza
Chryseobacterium meningosepticum
Stenotrophomonas maltophilia
Acinetobacter baumannii
Chryseobacterium meningosepticum
A 46-year-old dog warden was admitted to the hospital with several puncture bite wounds encountered while wrangling with a stray dog. Culture at 48 hours produced small yellow colonies on 5% sheep blood and chocolate agars in10% CO2, but no growth on MacConkey agar. Gram stain showed gram-negative curved, fusiform rods. Colonies were oxidase and catalase positive. What is the most likely identification?
Capnocytophaga canimorsus
Francisella tularensis
Legionella pneumophila
Pseudomonas aeruginosa
Capnocytophaga canimorsus
C. canimorsus are part of the oral flora of dogs.
The organisms require at least 5% CO2 for growth and grow slowly on blood and chocolate agars. Colonies can grow in 48 hours if cultured in high CO2 on BHI agar with 5% sheep blood.
A suspected case of Legionnaires’ disease was noted on the request form for a culture and sensitivity ordered on a sputum sample. The patient was a 70-year-old male who presented with a positive serological test for Legionella spp. What is the most efficient way to confirm the infection using the submitted sample?
Culture the sputum on MacConkey agar
Gram stain of the sputum
Acid-fast staining
Direct immunofluorescent microscopy
Direct immunofluorescent microscopy
Since culture can take up to 10 days, rapid diagnosis by direct immunofluorescence and DNA amplification are preferred.
Direct fluorescent antibody tests are not as sensitive as culture or PCR, but are specific and can be used to rapidly confirm a positive serological test, which may be positive in the absence of disease.
Which of the following organisms will display lipase activity on egg yolk agar?
Clostridium botulinum
Clostridium sporogenes
Clostridium novyi (A)
All of these options
All of these options
Identification of Clostridium tetani is based upon:
Gram stain of the wound site
Anaerobic culture of the wound site
Blood culture results
Clinical findings
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.
Cycloserine–cefoxitin-fructose agar (CCFA) is used for the recovery of:
Yersinia enterocolitica
Yersinia intermedia
Clostridium perfringens
Clostridium difficile
Clostridium difficile
The gram-positive non–spore-forming anaerobic rods most frequently recovered from blood cultures as a contaminant are:
Propionibacterium acnes
Clostridium perfringens
Staphylococcus intermedius
Veillonella parvula
Propionibacterium acnes
P. acnes is a nonspore former and is described as a diphtheroid-shaped rod. It is part of the normal skin, nasopharynx, genitourinary, and gastrointestinal tract flora but is implicated as an occasional cause of endocarditis.
A flexible calcium alginate nasopharyngeal swab is the collection device of choice for recovery of:
Staphylococcus aureus
Streptococcus pneumoniae
Corynebacterium diphtheriae
Bacteroides fragilis
Corynebacterium diphtheriae
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?
Mycobacterium tuberculosis
Mycobacterium ulcerans
Mycobacterium kansasii
Mycobacterium avium–intracellulare complex
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.
Individuals showing a positive purified protein derivative (PPD) skin test for M. tuberculosis are usually:
Infective
Symptomatic of pulmonary disease
Latently infected
Falsely positive
Latently infected
A positive PPD test indicates a person who is latently infected with M. tuberculosis. Such persons are asymptomatic and not infectious, but have a 10% risk of developing tuberculosis during their lifetime.
Which mycobacterium is associated with Crohn’s disease?
M. marinum
M. paratuberculosis
M. avium
M. gordonae
M. paratuberculosis
Routine laboratory testing for Treponema pallidum involves:
Culturing
Serological analysis
Acid-fast staining
Gram staining
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.
Which organism typically produces “fried-egg” colonies on agar within 1–5 days of culture from a genital specimen?
Mycoplasma hominis
Borrelia burgdorferi
Leptospira interrogans
Treponema pallidum
Mycoplasma hominis
Which procedure is appropriate for culture of genital specimens in order to recover Chlamydia spp.?
Inoculate cycloheximide-treated McCoy cells
Plate onto blood and chocolate agar
Inoculate into thioglycollate (THIO) broth
Plate onto modified Thayer–Martin agar within 24 hours
Inoculate cycloheximide-treated McCoy cells
Which of the following organisms are transmitted to animals and humans after a tick bite?
Leptospira
Chlamydia and Mycoplasma spp.
Neisseria sicca
Ehrlichia and Anaplasma spp.
Ehrlichia and Anaplasma spp.
What is the first step to be performed in the identification of an unknown yeast isolate?
Gram stain smear
India ink stain
Catalase test
Germ tube test
Germ tube test
The Hair Baiting Test is used to differentiate which two species of Trichophyton that produce red colonies on Sabouraud agar plates?
T. mentagrophytes and T. rubrum
T. tonsurans and T. schoenleinii
T. tonsurans and T. violaceum
T. verrucosum and T. rubrum
T. mentagrophytes and T. rubrum
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?
Candida albicans
Cryptococcus neoformans
Cryptococcus laurentii
Candida tropicalis
Cryptococcus neoformans
After a vacation to the Southwestern United States, a midwesterner complained of flulike symptoms with fever, chills, nonproductive cough, and chest pain. Microscopic exam of sputum, cleared with KOH, revealed large, thick-walled spherules containing endospores. Upon culture, the mold phase showed septate hyphae and alternating barrel-shaped arthroconidia. Which organism is most likely the cause of thispneumonia?
Coccidioides immitis
Histoplasma capsulatum
Paracoccidioides brasiliensis
Penicillium marneffei
Coccidioides immitis
Specimens for virus culture should be transported in media containing:
Antibiotics and 5% sheep blood
Saline and 5% sheep blood
22% bovine albumin
Antibiotics and nutrient
Antibiotics and nutrient
Media used for transporting specimens for viral culture are similar to those for bacteria with the addition of a nutrient such as fetal calf serum or albumin and antibiotics.
Which virus belonging to the Reoviridae group causes gastroenteritis in infants and young children but an asymptomatic infection in adults?
Coxsackie B virus
Rotavirus
Respiratory syncytial virus
Rhabdovirus
Rotavirus
A 40-year-old female experienced a respiratory infection after returning home from a visit to her homeland of China. A rapid onset of pneumonia in the lower respiratory area prompted the physician to place her in isolation. She was diagnosed presumptively with severe acute respiratory syndrome (SARS) and placed on a respirator. What type of testing should be done next to diagnose this disease?
Molecular technique and cell culture
Latex agglutination test
Blood culture
Complement fixation
Molecular technique and cell culture
