BOC MICROBIOLOGY COMPREHENSIVE
EXAMINATION TEST QUESTIONS AND
CORRECT ANSWERS COMPLETE SOLUTION
VERIFIED PASS
●● A sheep blood agar plate inoculated with 0.001mL of urine grows 70
colonies of Staphylococcus aureus. How many colony forming units per
mL of urine be reported?
a 70
b 700
c 7,000
d 70,000
Answer: d 70,000
d When 0.001 mL of urine is plated, the growth of one colony is
equivalent to 1000 CFU/mL. Thus 70 colonies is 70,000 CFU/mL.
●● The lowest concentration of antibiotic that inhibits growth of a test
that inhibits growth of a test organism is the:
a minimum inhibitory concentration
b serum inhibitory concentration
c minimum bactericidal titer
d maximum inhibitory titer
,Answer: a minimum inhibitory concentration
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.
●● Which of the following clean catch urine culture colony counts
indicates the patient likely has a urinary tract infection?
a 10^1 CFU/mL
b 10^3 CFU/mL
c 10^5 CFU/mL
d no growth
Answer: b 10^3 CFU/mL
b Patients with infection often have at least 100,000 bacteria/mL of urine
in the bladder. However one third of young women with symptomatic
cystitis have less than 100,000 bacteria/mL of urine. The Infectious
Disease Society of America consensus definition of cystitis is greater
than or equal to 1,000 CFU/mL of a uropathogen.
●● 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 100 C
d requires a source of ethylene oxide
Answer: a uses 15 lbs of pressure for 15 minutes
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.
●● 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
Answer: a 0 CFU/mL
a Urine in the bladder is normally sterile. Suprapubic aspiration removes
urine directly from the bladder and yields a specimen free of urethral
contamination.
●● An aspirate of a deep wound was plated on blood agar plates and
incubated aerobically and anaerobically. At 24 hours there was growth
on both plates. This indicates that the organism is
a(n):
, a nonfermenter
b obligate anaerobe
c aerobe
d facultative anaerobe
Answer: d facultative anaerobe
d Facultative anaerobes are organisms that can grow under both aerobic
and anaerobic conditions.
●● 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
Answer: c 1:10
c Human blood contains substances that may inhibit microbial growth.
Diluting blood in culture broth reduces the concentration of these
substances as well as any antibiotics that may be present. The
recommended blood broth ratio is 1:5-1:10. Dilutions less than this may
cause the blood to clot trapping organisms in the clot. Greater dilutions
may increase the time to detection
EXAMINATION TEST QUESTIONS AND
CORRECT ANSWERS COMPLETE SOLUTION
VERIFIED PASS
●● A sheep blood agar plate inoculated with 0.001mL of urine grows 70
colonies of Staphylococcus aureus. How many colony forming units per
mL of urine be reported?
a 70
b 700
c 7,000
d 70,000
Answer: d 70,000
d When 0.001 mL of urine is plated, the growth of one colony is
equivalent to 1000 CFU/mL. Thus 70 colonies is 70,000 CFU/mL.
●● The lowest concentration of antibiotic that inhibits growth of a test
that inhibits growth of a test organism is the:
a minimum inhibitory concentration
b serum inhibitory concentration
c minimum bactericidal titer
d maximum inhibitory titer
,Answer: a minimum inhibitory concentration
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.
●● Which of the following clean catch urine culture colony counts
indicates the patient likely has a urinary tract infection?
a 10^1 CFU/mL
b 10^3 CFU/mL
c 10^5 CFU/mL
d no growth
Answer: b 10^3 CFU/mL
b Patients with infection often have at least 100,000 bacteria/mL of urine
in the bladder. However one third of young women with symptomatic
cystitis have less than 100,000 bacteria/mL of urine. The Infectious
Disease Society of America consensus definition of cystitis is greater
than or equal to 1,000 CFU/mL of a uropathogen.
●● 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 100 C
d requires a source of ethylene oxide
Answer: a uses 15 lbs of pressure for 15 minutes
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.
●● 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
Answer: a 0 CFU/mL
a Urine in the bladder is normally sterile. Suprapubic aspiration removes
urine directly from the bladder and yields a specimen free of urethral
contamination.
●● An aspirate of a deep wound was plated on blood agar plates and
incubated aerobically and anaerobically. At 24 hours there was growth
on both plates. This indicates that the organism is
a(n):
, a nonfermenter
b obligate anaerobe
c aerobe
d facultative anaerobe
Answer: d facultative anaerobe
d Facultative anaerobes are organisms that can grow under both aerobic
and anaerobic conditions.
●● 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
Answer: c 1:10
c Human blood contains substances that may inhibit microbial growth.
Diluting blood in culture broth reduces the concentration of these
substances as well as any antibiotics that may be present. The
recommended blood broth ratio is 1:5-1:10. Dilutions less than this may
cause the blood to clot trapping organisms in the clot. Greater dilutions
may increase the time to detection
