CB Flashcards
Bacteria are: *
a. Unicellular, prokaryotic organisms
b. Multicellular, prokaryotic organisms
c. Unicellular, eukaryotic organisms
d. Multicellular, eukaryotic organisms
A
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 Unicellular, prokaryotic organisms
D
Among clinically relevant organisms, bacteria are singlecell 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
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 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
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
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
- Microorganisms that lack cell walls (commonly called
mycoplasmas and making up the class Mollicutes) and do
not synthesize the precursors of peptidoglycan.
The Quellung test depends on the antigenic specificity of
the: *
a. Capsule
b. Cell wall
c. Flagella
d. Nucleus
A
Which feature distinguishes Erysipelothrix rhusiopathiae
from other clinically significant non-spore-forming, grampositive, facultatively anaerobic bacilli? *
a. Tumbling motility
b. Beta-hemolysis
c. More pronounced motility at 25ºC than 37ºC
d. H2S production
D
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
A slimy colony on the blood agar medium indicates which
of the following characteristics may be present:*
a. Blood agar is too old
b. Organism has a capsule
c. Plate was incubated at too high temperature
d. Plate was incubated too long
B
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
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 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
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
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
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
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
The 2 most common causes of failure of GasPak system
is 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 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
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
- MTM: Modified Thayer-Martin Medium
- Vancomycin inhibits the growth of gram-positive bacteria
- Colistin inhibits the growth of gram-negative bacteria
except N. gonorrhoeae - Nystatin inhibits the growth of fungi
- 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
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
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
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
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 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
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
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
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
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
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
Human blood contains substance that may inhibit
microbial growth. Diluting blood in culture broth reduces the concentration of theses substances as well ass any antibiotics that may be present. The recommended bloodbroth 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
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
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 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
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% alcoho
D
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
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
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
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
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
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
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
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
- 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
- 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
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
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
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 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
- The gram stain and culture growth describe a
Staphylococcus species. Catalase production confirms
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 slide coagulase test. Organism:*
a. Produces only free coagulase and is S. aureus
b. Produces only bound coagulase and is S. aureus
c. Is S. epidermidis because of the negative slide test
d. Is S. epidermidis since the slide test is unreliable
A
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
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 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
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
Slime production is associated with which Staphylococcus
species?*
a. S. aureus
b. S. epidermidis
c. S. intermedius
d. S. saprophyticus
B
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
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 novobioci
B
Which of the following is not a member of family
Micrococcaceae?*
a. Staphylococcus
b. Streptococcus
c. Planococcus
d. Stomatococcus
B
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
By using a 15-μg erythromycin disk adjacent to a 2-μg
clindamycin disk in a disk diffusion procedure, 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
D
Green or brown color surrounding the colony:*
a. Alpha hemolysis
b. Beta hemolysis
c. Gamma hemolysis
d. Alpha prime hemolysis
A
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, 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
Gram-positive cocci in chains are seen on a Gram stain
from a blood culture. The organism grows as a betahemolytic 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 are
biochemical test for the presumptive or definitive
identification 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
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 (ToddHewitt 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
Viridans streptococci can be differentiated from
Streptococcus pneumoniae by:*
a. Alpha hemolysis
b. Morphology
c. Catalase
d. Bile solubility
D
Bile solubility testing of alpha hemolytic streptococci
differentiates S. pneumoniae (soluble) from other alphahemolytic 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
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. 2/2
b. ≥ 6 mm
c. ≥ 10 mm
d. ≥ 14 mm
e. ≥ 16 mm
D
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
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
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; alphahemolytic:*
a. Enterococcus faecalis
b. Leuconostoc sp.
c. Streptococcus pyogenes
d. Streptococcus pneumoniae
D
Necrotizing fasciitis is a serious infection associated with:*
a. Streptococcus agalactiae
b. Streptococcus mitis
c. Streptococcus pyogenes
d. Staphylococcus epidermidis
C
When streaking a throat culture on 5% sheep blood agar,
stabbing the agar plate provides enhanced detection for:
a. DNase activity
b. Streptolysin O
c. Streptolysin S
B
- Bile esculin hydrolysis
a. DNase activity
b. Streptolysin O
c. Streptolysin S
B
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
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
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
The PYR hydrolysis test is highly specific for group A
streptococci and group D enterococci. The test detects the
pyrrolidonylarylamidase enzyme, which hydrolyzes PYR.
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 MartinLewis agar
d. Culture specimens in ambient oxygen at 37°C
D
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
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
Colonies are gray, translucent, smooth, glistening; may
have dry, claylike consistency:*
a. Neisseria animaloris
b. Neisseria elongata
c. Moraxella lacunata
d. Moraxella catarrhalis
B
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
A penicillin-resistant Neisseria gonorrhoeae produces:*
a. Alpha-hemolysin
b. Beta-lactamase
c. Enterotoxin
d. Coagulase
B
Antimicrobial resistance in Neisseria gonorrhea is
widespread. The production of beta-lactamase
(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
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
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 sulfide (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
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
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 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 pinkcolored 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
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
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
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 p-dimethylaminobenzaldehyde (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
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
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 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 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
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
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 phosphatebuffered 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
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
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 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
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 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
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
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
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 POS
Urease NEG
PHE DA NEG
ORN AND LYS DA NEG
ARG DC NEG
Gel Hydrolysis POS
Indole NEG
VP POS
Citrate POS
a. Proteus vulgaris
b. Serratia
marcescens
c. Proteus mirabilis
d. Enterobacter
cloacae
B
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 lactose-negative, motile, gramnegative rods prior to antibiotic therapy. Given the
following biochemical reactions, which is most likely
organism?*
H2S (TSI) POS
VP NEG
DNase POS
Gel Hydrolysis POS
ORN DC Neg
Indole POS
Citrate NEG
PHE DA POS
MR POS
Urease POS
a. Proteus vulgaris
b. Proteus mirabilis
c. Serratia marcescens
d. Klebsiella pneumoniae
A
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
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
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 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 identification is very difficult.
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 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
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
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 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
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
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
d. 20% O2, 5% CO2, and 75% N2
A
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
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
- 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 multocida (P. canis) is part of the normal
mouth flora of cats and dogs and is frequently recovered
from wounds inflicted 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
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
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 requires exogenous X factor and causes genital
lesions referred to as “soft chancres.”
“Clue cells” are seen on a smear of vaginal discharge
obtained from an 18-year-old female emergency
department patient. This finding, along with 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
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
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
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
Fruity or grapelike smell, corn tortilla-like odor:*
a. Burkholderia cepacia
b. Pasteurella multocida
c. Proteus spp.
d. Pseudomonas aeruginosa
D
Musty or mushroom odor:*
a. Burkholderia cepacia
b. Pasteurella multocida
c. Proteus spp.
d. Pseudomonas aeruginosa
B
.Smell of ammonium cyanide (almond-like):*
a. Eikenella corrodens
b. Chromobacterium violaceum
c. Haemophilius influenzae
d. Stenotrophomonas maltophilia
B
.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
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
Both species of Bacillus are catalase and lecithinase
positive and produce acid from glucose. B. cereus is βhemolytic 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 βhemolytic 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
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
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
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 sheepblood agar anaerobically produces a double zone of βhemolysis and is positive for lecithinase. What is the
presumptive identification?
a. Bacteroides ureolyticus
b. Bacteroides fragilis
c. Clostridium perfringens
d. Clostridium difficile
C
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.
difficile 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
Egg yolk agar (modified 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
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
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
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
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
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
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 antibiotic-associated colitis?*
a. C. ramosum
b. C. difficile
c. C. perfringens
d. C. sporogenes
B
C. difficile 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.
5.Cycloserine–cefoxitin-fructose agar (CCFA) is used for the
recovery of:*
a. Yersinia enterocolitica
b. Yersinia intermedia
c. Clostridium perfringens
d. Clostridium difficile
D
CCFA is used for recovery of C. difficile
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
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
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. 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
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
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
*Streptococci
1. Gram positive cocci in chains
2. Nonmotile
3. Catalase negative
*Listeria
1. Gram positive bacilli
2. Motile
3. 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
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. 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-year-old 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
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. should be suspected if colonies that are
partially acid fast by the traditional method are positive
with the modified 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
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
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
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
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
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
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
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
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 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 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
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 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 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 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
b. M. ulcerans
c. M. marinum
d. M. avium–intracellulare complex
A
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. 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
Lyme disease may result in acute arthritis and meningitis
and is caused by B. burgdorfer
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
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 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
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 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
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
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
Correct answer: 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
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 identification of U. urealyticum.
Which of the following organisms are transmitted to
animals and humans after a tick bite?*
a. Leptospira
b. Chlamydia and Mycoplasma spp.
c. Neisseria sicca
d. Ehrlichia and Anaplasma spp.
D
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.
Outbreak of food poisoning leads to diarrhea in multiple patients. What should be done to investigate the cause of the outbreak?
a. Disk diffusion
b. Catalase
c. Coagulase
d. Phage typing
D. Phage typing
Detection of a single strain of bacteria
(+) Plaque formation/ lysis
Organism and Etiology
1. Chancroid
2. Chancre
- looks like chancre; soft painful (H. ducreyi)
- hard, painless (T. pallidum)
- Spindle-shaped with gliding motility
- Curve comma-shaped with rapid darting/ “shooting star” motility; polar peritrichous flagella
- Resemble seagull app; darting motility, polar/ monotrichous flagellum
- Resemble seagull app; lophotrichous flagella; gastric ulcer, rapid urease (+)
- Capnocytophaga
- Vibrio cholerae
- Campylobacter
- Helicobacter pylori
- Rapid test for H. pylori
- Diagnostic test for H. pylori
- Rapid breath test
- Gastric biopsy –> Rapid urease (+)
- Bamboo pole appearance (bacilli in chains)
- Pallisades, resemble picket fences/ cigarette packet (“Action star”)
- Bacillus anthracis
- Corynebacterium diphtheriae
C. diptheriae = ACTION STAR
- GUN: gun metal black colony on CTBA
- CIGARETTE: Arrangement
- BABES: Babes Ernst granules (metachromatic granules)
- BULL: Bull’s neck appearance
- Smallest nonpathogenic bacteria
- Smallest pathogenic bacteria
- Largest nonpathogenic bacteria
- Largest pathogenic bacteria
- Longest bacteria
- Mycoplasma pneumoniae
- Haemophilus ducreyi
- Thiomargarita namibiensis
- Bacillus anthacis
- Borrelia burgdorferi (10um)
Virulence
1. Shigella-like infection
2. Shigella
- EIEC > or = 100,000 CFU/mL – explosive stool
- 100-200 CFU/mL – dysentery (bloody diarrhea), scanty bloody stool
- Agent of Lock jaw
- Most potent exotoxin
- Clostridium tetani
- Botulinum toxin
Produces toxin except:
a. Neisseria
b. Clostridium
c. Escherichia
d. Salmonella
a. Neisseria
A. Neisseria – No exotoxin with endotoxin
B. gm (+) no endotoxin
C. D. gm (-) with exotoxin and endotoxin
All gm (-) are endotoxins not produced but are already in the membrane (Neisseria, Escherichia, Salmonella)
Opportunistic pathogen which possesses exotoxin A and causes respiratory infection in cystic fibrosis patients
P. aeruginosa > B. cepacia > S. maltophilia
Oxidizers infect lungs
- What is the most important PPE?
- HBV needlestick percentage
- HIV needlestick percentage
- What is not a PPE?
- Gloves
- 30%
- 0.03%
- Hand sanitizer
Recipient cell uptake of naked (free) DNA released into the environment when another bacterial cell (i.e., donor) dies and undergoes lysis:
Process is mediated through viruses capable of infecting bacteria (i.e., bacteriophages):
Process occurs between two living cells, involves cell-to-cell contact, and requires mobilization of the donor bacterium’s chromosome
Conjugation
Transduction
Transformation
Transformation
Transduction
Conjugation
