BOC Microbiology Final Exam 2022 Study Guide with
complete solution
d (Chocolate agar and chocolate agar-based selective media should be used for
recovery of Neisseria gonorrhoeae from urethral discharge. Chocolate agar
provides the nutrients required by N gonorrhoeae and selective media contains
antimicrobial agents that inhibits other organisms and permits recovery of
pathogenic Neisseria.)
1) Proper media for culture of a urethral discharge from a man include:
a. sheep blood and phenylethyl alcohol agars
b. eosin methylene blue and sheep blood agars
c. thioglycollate broth and chocolate agar
d. chocolate agar and modified Thayer Martin agar
d (When 0.001 mL of urine is plated, the growth of one colony is equivalent to
1000 CPU/mL. Thus 70 colonies is 70,000 CPU/mL.)
2) A sheep blood agar plate inoculated with 0.001 mL of urine grows 70 colonies of
Staphylococcus aureus. How many colony forming units per mL of urine should be
reported:
a. 70
b. 700
c. 7000
d. 70000
a (The MIC is a basic laboratory measurement of the activity of an antibiotic
against an organism. It is the lowest concentration of antibiotic that inhibits
visible growth of the organism. It does not represent the concentration of
antibiotic that is lethal to the organism.)
3) The lowest concentration of antibiotic that inhibits growth of a test organism is the :
a. minimum inhibitory concentration
b. serum inhibitory concentration
c. minimum bactericidal titer
d. minimum inhibitory titer
a (The traditional gravity displacement steam sterilization cycle is 121 C for 15
minutes at 15 pounds per square inch. Ethylene oxide is an alternative
sterilization method.)
5) 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 minimum temp of 100 C
d. requires a source of ethylene oxide
a (Urine in the bladder is normally sterile. Suprapubic aspiration removes urine
directly from the bladder and yields a specimen free of urethral contamination.)
6) The expected colony count in a suprapubic urine from a healthy individual is:
a. 0 CFU/mL
b. 100 CFU/mL
,c. 1,000 CFU/mL
d. 100,000 CFU/mL
d (Facultative anaerobes are organisms that can grow under both aerobic and
anaerobic conditions.)
7) An aspirate of a deep wound was plated on blood agar plates and incubated
aerobically and anaerobically. At 24 hrs. there was growth on both plates. This indicates
that the organism is a:
a. nonfermenter
b. obligate anaerobe
c. aerobe
d. facultative anaerobe
b (Antimicrobial resistance in Neisseria gonorrhoeae is widespread. The
production of beta-lactamase [penicillinase] breaks open the beta lactam ring of
penicillin, destroying its activity. Thus, N. gonorrhoeae that produce beta
lactamase are resistant to penicillin.)
9) A penicillin resistant Neisseria gonorrhoeae produces:
a. alpha-hemolysin
b. beta-lactamase
c. enterotoxin
d. coagulase
a (Columbia CNA agar contains colistin and nalidixic acid, which inhibit most
gram-negative organisms. Eosin methylene blue is selective and inhibits gram-
positive organisms and modified Thayer Martin is selective and inhibits gram-
positive organisms, gram-negative bacilli and yeast.)
10) Which selective medium is used for the isolation of gram-positive microorganisms?
a. Columbia CNA with 5% sheep blood
b. trypticase soy agar with 5% sheep blood
c. eosin methylene blue
d. modified Thayer-Martin
d (The chromogenic cephalosporin test using nitrocefin is the most sensitive and
specific test for detection of beta lactamase. Acidimetric tests employing
penicillin are less expensive, but not as sensitive, as the nitrocefin assay.)
11) The most sensitive substrate for the detection of beta-lactamases is:
a. penicillin
b. ampicillin
c. cefoxitin
d. nitrocefin
a (Systemic enterococcal infections, such as endocarditis, are commonly treated
with a cell-wall-active agent and an aminoglycoside. These agents act
synergistically to kill the organism. If the organism is resistant to one or both,
there is no synergy, and the combination will fail. It is important to detect
aminoglycoside and beta-lactam resistance in these cases. Enterococci have
intrinsic moderate level resistance to aminoglycosides. Acquired resistance
corresponds to very high MICs [greater than 500 mg/mL] for gentamicin and is
termed high level resistance.)
,13) An Enterococcus isolated from multiple blood cultures in a patient with endocarditis
should be:
a. screened for high level aminoglycoside resistance
b. checked for tolerance
c. assayed for serum antimicrobial activity
d. tested for beta-lactamase production
c (Variations in the concentrations of divalent cations primarily calcium and
magnesium affect the results of aminoglycoside, tetracycline and colistin tests
with P aeruginosa isolates. A cation concentration that is too high results in
smaller zone sizes, and a concentration that is too low increases zone sizes.)
14) In the Kirby-Bauer disk diffusion susceptibility test, which variable is critical when
testing Pseudomonas species for antibiotic susceptibility to aminoglycosides?
a. incubation temp
b. duration of incubation
c. cation content of media
d. depth of agar
d (Cefoxitin is used as a surrogate for mecA-mediated oxacillin resistance in S
aureus. S aureus with cefoxitin MICs >4 mg/mL are considered oxacillin resistant.
The Clinical Laboratory Standards Institute [CLSI] recommends addition of 2%
NaCl, incubation at 35 +/- 2 C, and incubation for 24 hours when performing
susceptibility testing of S aureus against oxacillin.)
15) The procedure that assures the most accurate detection of mecA-mediated oxacillin
resistance in routine broth microdilution susceptibility testing against S aureus is:
a. addition of 4% NaCl
b. incubation at 30 C
c. incubation for 48 hrs.
d. use of cefoxitin for testing
c (All Mueller-Hinton agar used for disk diffusion susceptibility testing should be
poured to a depth of 4 mm. If the depth of the media is < 4 mm, this may be
associated with excessively large zones and false-positive susceptibility results.
Agar that is > 4 mm in depth may cause excessively small zone sizes.)
17) 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
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.)
, 18) 3 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 a low grade bacteria infection
b. the organism is most likely a contaminant
c. the patient has a line infection
d. the blood culture bottles are defective
a (Campylobacter coli/jejuni require a microaerophilic atmosphere for optimal
recovery. The use of selective media is recommended for recovery from fecal
specimens. Selective media for Campylobacter contains antibiotics to inhibit the
growth of enteric gram-negative flora. Unlike other enteric pathogens, C
coli/jejuni grow well at
42 C.)
19) In order to isolate Campylobacter coli/jejuni the fecal specimen should be:
a. inoculated onto selective plating media and incubated in reduced oxygen with added
CO2 at 42 C
b. stored in tryptic soy broth before plating to ensure growth of the organism
c. inoculated onto selective plating media and incubated at both 35 C and at room temp
d. incubated at 35 C for 2 hrs. in Cary-Blair media before inoculating onto selective
plating media
a (Due to the small size of viruses, they are not visible using light microscopy.
Electron microscopy is used to visualize viruses and the internal structure of
microorganisms.)
21) Which type of microscope would be most useful in examining viruses and the
structure of microbial cells?
a. electron
b. phase-contrast
c. dark-field
d. bright-field
b (Daily disk diffusion quality control can be converted to weekly testing when 30
days of consecutive testing demonstrates no more than 3 antibiotic/organism
combinations outside of the acceptable limits.)
22) 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 (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.)
23) In disk diffusion susceptibility testing, as a antimicrobial agent diffuses away from
the disk, the concentration antibiotic is:
a. increased
complete solution
d (Chocolate agar and chocolate agar-based selective media should be used for
recovery of Neisseria gonorrhoeae from urethral discharge. Chocolate agar
provides the nutrients required by N gonorrhoeae and selective media contains
antimicrobial agents that inhibits other organisms and permits recovery of
pathogenic Neisseria.)
1) Proper media for culture of a urethral discharge from a man include:
a. sheep blood and phenylethyl alcohol agars
b. eosin methylene blue and sheep blood agars
c. thioglycollate broth and chocolate agar
d. chocolate agar and modified Thayer Martin agar
d (When 0.001 mL of urine is plated, the growth of one colony is equivalent to
1000 CPU/mL. Thus 70 colonies is 70,000 CPU/mL.)
2) A sheep blood agar plate inoculated with 0.001 mL of urine grows 70 colonies of
Staphylococcus aureus. How many colony forming units per mL of urine should be
reported:
a. 70
b. 700
c. 7000
d. 70000
a (The MIC is a basic laboratory measurement of the activity of an antibiotic
against an organism. It is the lowest concentration of antibiotic that inhibits
visible growth of the organism. It does not represent the concentration of
antibiotic that is lethal to the organism.)
3) The lowest concentration of antibiotic that inhibits growth of a test organism is the :
a. minimum inhibitory concentration
b. serum inhibitory concentration
c. minimum bactericidal titer
d. minimum inhibitory titer
a (The traditional gravity displacement steam sterilization cycle is 121 C for 15
minutes at 15 pounds per square inch. Ethylene oxide is an alternative
sterilization method.)
5) 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 minimum temp of 100 C
d. requires a source of ethylene oxide
a (Urine in the bladder is normally sterile. Suprapubic aspiration removes urine
directly from the bladder and yields a specimen free of urethral contamination.)
6) The expected colony count in a suprapubic urine from a healthy individual is:
a. 0 CFU/mL
b. 100 CFU/mL
,c. 1,000 CFU/mL
d. 100,000 CFU/mL
d (Facultative anaerobes are organisms that can grow under both aerobic and
anaerobic conditions.)
7) An aspirate of a deep wound was plated on blood agar plates and incubated
aerobically and anaerobically. At 24 hrs. there was growth on both plates. This indicates
that the organism is a:
a. nonfermenter
b. obligate anaerobe
c. aerobe
d. facultative anaerobe
b (Antimicrobial resistance in Neisseria gonorrhoeae is widespread. The
production of beta-lactamase [penicillinase] breaks open the beta lactam ring of
penicillin, destroying its activity. Thus, N. gonorrhoeae that produce beta
lactamase are resistant to penicillin.)
9) A penicillin resistant Neisseria gonorrhoeae produces:
a. alpha-hemolysin
b. beta-lactamase
c. enterotoxin
d. coagulase
a (Columbia CNA agar contains colistin and nalidixic acid, which inhibit most
gram-negative organisms. Eosin methylene blue is selective and inhibits gram-
positive organisms and modified Thayer Martin is selective and inhibits gram-
positive organisms, gram-negative bacilli and yeast.)
10) Which selective medium is used for the isolation of gram-positive microorganisms?
a. Columbia CNA with 5% sheep blood
b. trypticase soy agar with 5% sheep blood
c. eosin methylene blue
d. modified Thayer-Martin
d (The chromogenic cephalosporin test using nitrocefin is the most sensitive and
specific test for detection of beta lactamase. Acidimetric tests employing
penicillin are less expensive, but not as sensitive, as the nitrocefin assay.)
11) The most sensitive substrate for the detection of beta-lactamases is:
a. penicillin
b. ampicillin
c. cefoxitin
d. nitrocefin
a (Systemic enterococcal infections, such as endocarditis, are commonly treated
with a cell-wall-active agent and an aminoglycoside. These agents act
synergistically to kill the organism. If the organism is resistant to one or both,
there is no synergy, and the combination will fail. It is important to detect
aminoglycoside and beta-lactam resistance in these cases. Enterococci have
intrinsic moderate level resistance to aminoglycosides. Acquired resistance
corresponds to very high MICs [greater than 500 mg/mL] for gentamicin and is
termed high level resistance.)
,13) An Enterococcus isolated from multiple blood cultures in a patient with endocarditis
should be:
a. screened for high level aminoglycoside resistance
b. checked for tolerance
c. assayed for serum antimicrobial activity
d. tested for beta-lactamase production
c (Variations in the concentrations of divalent cations primarily calcium and
magnesium affect the results of aminoglycoside, tetracycline and colistin tests
with P aeruginosa isolates. A cation concentration that is too high results in
smaller zone sizes, and a concentration that is too low increases zone sizes.)
14) In the Kirby-Bauer disk diffusion susceptibility test, which variable is critical when
testing Pseudomonas species for antibiotic susceptibility to aminoglycosides?
a. incubation temp
b. duration of incubation
c. cation content of media
d. depth of agar
d (Cefoxitin is used as a surrogate for mecA-mediated oxacillin resistance in S
aureus. S aureus with cefoxitin MICs >4 mg/mL are considered oxacillin resistant.
The Clinical Laboratory Standards Institute [CLSI] recommends addition of 2%
NaCl, incubation at 35 +/- 2 C, and incubation for 24 hours when performing
susceptibility testing of S aureus against oxacillin.)
15) The procedure that assures the most accurate detection of mecA-mediated oxacillin
resistance in routine broth microdilution susceptibility testing against S aureus is:
a. addition of 4% NaCl
b. incubation at 30 C
c. incubation for 48 hrs.
d. use of cefoxitin for testing
c (All Mueller-Hinton agar used for disk diffusion susceptibility testing should be
poured to a depth of 4 mm. If the depth of the media is < 4 mm, this may be
associated with excessively large zones and false-positive susceptibility results.
Agar that is > 4 mm in depth may cause excessively small zone sizes.)
17) 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
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.)
, 18) 3 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 a low grade bacteria infection
b. the organism is most likely a contaminant
c. the patient has a line infection
d. the blood culture bottles are defective
a (Campylobacter coli/jejuni require a microaerophilic atmosphere for optimal
recovery. The use of selective media is recommended for recovery from fecal
specimens. Selective media for Campylobacter contains antibiotics to inhibit the
growth of enteric gram-negative flora. Unlike other enteric pathogens, C
coli/jejuni grow well at
42 C.)
19) In order to isolate Campylobacter coli/jejuni the fecal specimen should be:
a. inoculated onto selective plating media and incubated in reduced oxygen with added
CO2 at 42 C
b. stored in tryptic soy broth before plating to ensure growth of the organism
c. inoculated onto selective plating media and incubated at both 35 C and at room temp
d. incubated at 35 C for 2 hrs. in Cary-Blair media before inoculating onto selective
plating media
a (Due to the small size of viruses, they are not visible using light microscopy.
Electron microscopy is used to visualize viruses and the internal structure of
microorganisms.)
21) Which type of microscope would be most useful in examining viruses and the
structure of microbial cells?
a. electron
b. phase-contrast
c. dark-field
d. bright-field
b (Daily disk diffusion quality control can be converted to weekly testing when 30
days of consecutive testing demonstrates no more than 3 antibiotic/organism
combinations outside of the acceptable limits.)
22) 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 (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.)
23) In disk diffusion susceptibility testing, as a antimicrobial agent diffuses away from
the disk, the concentration antibiotic is:
a. increased
