BOC Microbiology Test Questions and Answers Rated A
Proper media for culture of a urethral discharge from colony counts indicates the patient likely has a
a man include: urinary tract infection?
a sheep blood and phenylethyl alcohol agars b eosin- a 10^1 CFU/mL
methylene blue and sheep blood agars b 10^3 CFU/mL
c thioglycollate broth and chocolate agar c 10^5 CFU/mL
d chocolate and modified Thayer-Martin agars - d no growth - ANSWER -b 10^3 CFU/mL
ANSWER -d chocolate and modified Thayer-
Martin agars b Patients with infection often have at least 100,000
bacteria/mL of urine in the bladder. However one
d Chocolate agar and chocolate agar- based third of young women with symptomatic cystitis have
selective media should be used for recovery of less than 100,000 bacteria/mL of urine. The
Neisseria gonorrhoeae from urethral discharge. Infectious Disease Society of America consensus
Chocolate agar provides the nutrients required by N definition of cystitis is greater than or equal to 1,000
gonorrhoeae and selective media contains CFU/mL of a uropathogen.
antimicrobial agents that inhibits other organisms and
permits recovery of pathogenic Neisseria.
The steam autoclave method of sterilization:
a uses 15 lbs of pressure for 15 minutes
A sheep blood agar plate inoculated with 0.001mL of b utilizes dry heat for 20 minutes
urine grows 70 colonies of Staphylococcus aureus. c produces a maximum temperature of 100 C
How many colony forming units per mL of urine be d requires a source of ethylene oxide -
reported? ANSWER -a uses 15 lbs of pressure for 15
a 70 minutes
b 700
c 7,000 a The traditional gravity displacement steam
d 70,000 - ANSWER -d 70,000 sterilization cycle is 121°C for 15 minutes at 15
pounds per square inch. Ethylene oxide is an
d When 0.001 mL of urine is plated, the growth of alternative sterilization method.
one colony is equivalent to 1000 CFU/mL. Thus 70
colonies is 70,000 CFU/mL.
The expected colony count in a suprapubic urine from
a healthy individual is:
The lowest concentration of antibiotic that inhibits a 0 CFU/mL
growth of a test that inhibits growth of a test b 100 CFU/mL
organism is the: c 1,000 CFU/mL
a minimum inhibitory concentration d 100,000 CFU/mL - ANSWER -a 0 CFU/mL
b serum inhibitory concentration
c minimum bactericidal titer a Urine in the bladder is normally sterile. Suprapubic
d maximum inhibitory titer - ANSWER -a aspiration removes urine directly from the bladder
minimum inhibitory concentration and yields a specimen free of urethral contamination.
a The MIC is a basic laboratory measurement of the
activity of an antibiotic against an organism. It is the An aspirate of a deep wound was plated on blood
lowest concentration of antibiotic that inhibits visible agar plates and incubated aerobically and
growth of the organism. It does not represent the anaerobically. At 24 hours there was growth on both
concentration of antibiotic that is lethal to the plates. This indicates that the organism is
organism. a(n):
a nonfermenter
b obligate anaerobe
Which of the following clean catch urine culture c aerobe
, BOC Microbiology Test Questions and Answers Rated A
d facultative anaerobe - ANSWER -d facultative positive organisms and modified Thayer Martin is
anaerobe selective and inhibits gram-positive organisms, gram-
negative bacilli and yeast.
d Facultative anaerobes are organisms that can grow
under both aerobic and anaerobic conditions.
The most sensitive substrate for the detection of
beta-lactamases is:
The proper blood-to-broth ratio for blood cultures to a penicillin
reduce the antibacterial effect of serum in adults is: b ampicillin
a 1:2 c cefoxitin
b 1:3 d nitrocefin - ANSWER -d nitrocefin
c 1:10
d 1:30 - ANSWER -c 1:10 d The chromogenic cephalosporin test using
nitrocefin is the most sensitive and specific test for
c Human blood contains substances that may inhibit detection of beta lactamase. Acidimetric tests
microbial growth. Diluting blood in culture broth employing penicillin are less expensive, but not as
reduces the concentration of these substances as sensitive, as the nitrocefin assay.
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 A Staphilococcus aureus isolate has an MIC of
organisms in the clot. Greater dilutions may increase 4ug/m: to axacillin. There is uncertainty as to whether
the time to detection this represents an oxacillin (heteroresistant) resistant
strain or a hyperproducer of beta-lactamase.
Strain Oxacillin Amoxicillin-clavulanic acid
A penicillin-resistant Neisseria gonorrhoeae strand A Sus Sus
produces: stand B Sus Res
a alpha-hemolysin strand C Res Sus
b beta-lactamase strand D Res Res
c enterotoxin Based on the above results for oxacillin and
d coagulase - ANSWER -b beta-lactamase amoxicillin, which strand is heteroresistant?
a strand A
b Antimicrobial resistance in Neisseria gonorrhoeae b strand B
is widespread. The production of beta-lactamase c strand C
(penicillinase) breaks open the beta lactam ring of d strand D - ANSWER -d strand D
penicillin, destroying its activity. Thus, Ngonorrhoeae
that produce beta lactamase are resistant to d A Staphylococcus aureus isolate with an MIC of 4
penicillin. pg/mL is resistant to oxacillin.. As per the Clinical and
Laboratory Standards Institute (CLSI)
recommendations a heteroresistant strain would be
Which selective medium is used for the isolation of defined as a methicillin (oxacillin) resistant S aureus
gram-positive microorganisms? (MRSA/ORSA). An MRSA/ORSA isolate would be
a Columbia CNA with 5% sheep blood reported as resistant to all beta lactam agents, beta
b trypticase soy agar with 5% sheep blood lactam/beta lactamase inhibitor combinations, such
c eosin methylene blue as amoxicillin- clavulanic acid, and carbapenems.
d modified Thayer-Martin - ANSWER -a
Columbia CNA with 5% sheep blood
13 An Enterococcus isolated from multiple blood
a Columbia CNA agar contains colistin and nalidixic cultures in a patient endocarditis should be:
acid, which inhibit most gram-negative organisms. a screened for high level aminoglycoside resistance
Eosin methylene blue is selective and inhibits gram- b checked for tolerance
, BOC Microbiology Test Questions and Answers Rated A
c assayed for serum antimicrobial activity resistant. The Clinical Laboratory Standards Institute
d tested for beta-lactamase production - (CLSI) recommends addition of 2% NaCl, incubation
ANSWER -a screened for high level at 35±2°C, and incubation for 24 hours when
aminoglycoside resistance performing susceptibility testing of S aureus against
oxacillin.
a Systemic enterococcal infections, such as
endocarditis, are commonly treated with a cell-wall-
active agent and an aminoglycoside. When performing a stool culture, a colony type typical
These agents act synergistically to kill the organism. of an enteric pathogen is subcultured on a blood agar
plate. The resulting pure culture is screened with
If the organism is resistant to one or both, there is no
synergy, and the combination will fail. It is importantseveral tests to obtain the following results:
to detect aminoglycoside and beta-lactam resistance TSI: acid butt, alkaline slant, no gas, no H2S
in these cases. Enterococci have intrinsic moderate phenylalanine deaminase: negative motility: positive
level resistance to aminoglycosides. Acquired serological typing: Shigella flexneri (Shigella
resistance corresponds to very high MICs (greater subgroup B)
than 500 pg/mL) for gentamicin and is termed high The serological typing is verified with new kit and
level resistance. controls. The best course of action would be to:
a report the organism as Shigella flexneri without
further testing
In the Kirby-Bauer disc diffusion susceptibility test, b verify reactivity of motility medium with positive and
which variable is critical when testing Pseudomonas negative controls
species for antibiotic susceptibility to c verify reactivity of the TSI slants with
aminoglycosides? positive and negative controls for H2S
a incubation temperature production
b duration of incubation d verify reactivity of phenylalanine d
c cation content of media aminase with positive and negative controls -
d depth of agar - ANSWER -c cation content of ANSWER -b verify reactivity of motility medium
media with positive and negative controls
c Variations in the concentrations of divalent cations b All of the biochemical and serological
primarily calcium and magnesium affect the results of reactions listed are consistent with an identification of
aminoglycoside, tetracycline and colistin tests with P Shigella flexneri, with the exception of motility. All
aeruginosa isolates. A cation concentration that is Shigella are nonmotile.
too high results in smaller zone sizes, and a
concentration that is too low increases zone sizes.
Susceptibility testing performed on quality control
organisms using a new media lot number yielded
The procedure that assures the most accurate zone sizes that were too large for all antibiotics
detection of mecA-mediated oxacillin resistance in tested. The testing was repeated using media from a
routine broth microdilution susceptibility testing previously used lot number, and all zone sizes were
against S aureus is: acceptable. Which of the following best explains the
a addition of 4% NaCl unacceptable zone sizes?
b incubation at 30°C a the antibiotic disks were not stored with the proper
c incubation for 48 hours desiccant
d use of cefoxitin for testing - ANSWER -d use b the depth of the media was too thick
of cefoxitin for testing c the depth of the media was too thin
d the antibiotic disks were not properly applied to the
d Cefoxitin is used as a surrogate for mecA-mediated media - ANSWER -c the depth of the media
oxacillin resistance in S aureus. S aureus with was too thin
cefoxitin MICs >4 pg/mL are considered oxacillin
, BOC Microbiology Test Questions and Answers Rated A
c All Mueller-Hinton agar used for disk selective media is recommended for recovery from
diffusion susceptibility testing should be poured to a fecal specimens. Selective media for Campylobacter
depth of 4mm. If the depth of the media is <4mm, this contains antibiotics to inhibit the growth of enteric
may be associated with excessively large zones and gram-negative flora. Unlike other enteric pathogens,
false- positive susceptibility results. Agar that is C coli/jejuni grow well at 42°C.
>4mm in depth may cause excessively small zone
sizes.
An expectorated sputum is sent to the laboratory for
culture from a patient with respiratory distress. The
Three sets of blood cultures were obtained from an Gram stain of the specimen shows many squamous
adult patient with fever and suspected endocarditis. epithelial cells (>25/lpf) and rare neutrophils. The
The aerobic bottle of one set had growth of microscopic appearance of the organisms present
Staphylococcus epidermidis at 5 days of incubation. include:
This indicates that: moderate gram-positive cocci in chains and
a there was low-grade bacteremia diplococci moderate gram-negative diplococci
b the organism is most likely a contaminant moderate palisading gram-positive bacilli all in
c the patient has a line infection moderate amounts
d the blood culture bottles are defective - This Gram stain is most indicative of:
ANSWER -b the organism is most likely a a a pneumococcal pneumonia
contaminant b an anaerobic infection
c an Haemophilus pneumonia
b Coagulase-negative staphylococci are commonly d oropharyngeal flora - ANSWER -d
associated with contaminated blood cultures; oropharyngeal flora
however, they are also increasing as a cause of true
bacteremia. Significant bacteremia in a patient with d Sputum specimen quality is assessed to determine
endocarditis is usually continuous and low grade. In if the specimen is representative of the site of
most cases, all blood cultures drawn will yield infection. The presence of white blood cells is an
positive results. The facts that only 1 bottle of 1 set indicator of infection, and presence of squamous
was positive, and that the bottle did not become epithelial cells is an indicator of oropharyngeal
positive until day 5 of incubation, indicate that this contamination.
isolate is most likely a contaminant. In this specimen, >25 epithelial cells per low power
field is an indicator of poor specimen quality, and the
bacteria present are representative of oropharyngeal
In order to isolate Campylobacter coli/jejuni, the fecal flora.
specimen should be:
a inoculated onto selective plating media and
incubated in reduced oxygen with added CO2 at Which type of microscope would be most useful in
42°C examining viruses and the structure of microbial
b stored in tryptic soy broth before plating to ensure cells?
growth of the organism a electron
c inoculated onto selective plating media and b phase-contrast
incubated at both 35°C and at room temperature c dark-field
d incubated at 35°C for 2 hours in Cary-Blair media d bright-fleld - ANSWER -a electron
before inoculating onto selective plating media -
ANSWER -a inoculated onto selective plating a Due to the small size of viruses, they are
media and incubated in reduced oxygen with added not visible using light microscopy. Electron
CO2 at 42°C microscopy is used to visualize viruses and the
internal structure of microorganisms.
a Campylobacter coli/jejuni require a microaerophilic
atmosphere for optimal recovery. The use of
Proper media for culture of a urethral discharge from colony counts indicates the patient likely has a
a man include: urinary tract infection?
a sheep blood and phenylethyl alcohol agars b eosin- a 10^1 CFU/mL
methylene blue and sheep blood agars b 10^3 CFU/mL
c thioglycollate broth and chocolate agar c 10^5 CFU/mL
d chocolate and modified Thayer-Martin agars - d no growth - ANSWER -b 10^3 CFU/mL
ANSWER -d chocolate and modified Thayer-
Martin agars b Patients with infection often have at least 100,000
bacteria/mL of urine in the bladder. However one
d Chocolate agar and chocolate agar- based third of young women with symptomatic cystitis have
selective media should be used for recovery of less than 100,000 bacteria/mL of urine. The
Neisseria gonorrhoeae from urethral discharge. Infectious Disease Society of America consensus
Chocolate agar provides the nutrients required by N definition of cystitis is greater than or equal to 1,000
gonorrhoeae and selective media contains CFU/mL of a uropathogen.
antimicrobial agents that inhibits other organisms and
permits recovery of pathogenic Neisseria.
The steam autoclave method of sterilization:
a uses 15 lbs of pressure for 15 minutes
A sheep blood agar plate inoculated with 0.001mL of b utilizes dry heat for 20 minutes
urine grows 70 colonies of Staphylococcus aureus. c produces a maximum temperature of 100 C
How many colony forming units per mL of urine be d requires a source of ethylene oxide -
reported? ANSWER -a uses 15 lbs of pressure for 15
a 70 minutes
b 700
c 7,000 a The traditional gravity displacement steam
d 70,000 - ANSWER -d 70,000 sterilization cycle is 121°C for 15 minutes at 15
pounds per square inch. Ethylene oxide is an
d When 0.001 mL of urine is plated, the growth of alternative sterilization method.
one colony is equivalent to 1000 CFU/mL. Thus 70
colonies is 70,000 CFU/mL.
The expected colony count in a suprapubic urine from
a healthy individual is:
The lowest concentration of antibiotic that inhibits a 0 CFU/mL
growth of a test that inhibits growth of a test b 100 CFU/mL
organism is the: c 1,000 CFU/mL
a minimum inhibitory concentration d 100,000 CFU/mL - ANSWER -a 0 CFU/mL
b serum inhibitory concentration
c minimum bactericidal titer a Urine in the bladder is normally sterile. Suprapubic
d maximum inhibitory titer - ANSWER -a aspiration removes urine directly from the bladder
minimum inhibitory concentration and yields a specimen free of urethral contamination.
a The MIC is a basic laboratory measurement of the
activity of an antibiotic against an organism. It is the An aspirate of a deep wound was plated on blood
lowest concentration of antibiotic that inhibits visible agar plates and incubated aerobically and
growth of the organism. It does not represent the anaerobically. At 24 hours there was growth on both
concentration of antibiotic that is lethal to the plates. This indicates that the organism is
organism. a(n):
a nonfermenter
b obligate anaerobe
Which of the following clean catch urine culture c aerobe
, BOC Microbiology Test Questions and Answers Rated A
d facultative anaerobe - ANSWER -d facultative positive organisms and modified Thayer Martin is
anaerobe selective and inhibits gram-positive organisms, gram-
negative bacilli and yeast.
d Facultative anaerobes are organisms that can grow
under both aerobic and anaerobic conditions.
The most sensitive substrate for the detection of
beta-lactamases is:
The proper blood-to-broth ratio for blood cultures to a penicillin
reduce the antibacterial effect of serum in adults is: b ampicillin
a 1:2 c cefoxitin
b 1:3 d nitrocefin - ANSWER -d nitrocefin
c 1:10
d 1:30 - ANSWER -c 1:10 d The chromogenic cephalosporin test using
nitrocefin is the most sensitive and specific test for
c Human blood contains substances that may inhibit detection of beta lactamase. Acidimetric tests
microbial growth. Diluting blood in culture broth employing penicillin are less expensive, but not as
reduces the concentration of these substances as sensitive, as the nitrocefin assay.
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 A Staphilococcus aureus isolate has an MIC of
organisms in the clot. Greater dilutions may increase 4ug/m: to axacillin. There is uncertainty as to whether
the time to detection this represents an oxacillin (heteroresistant) resistant
strain or a hyperproducer of beta-lactamase.
Strain Oxacillin Amoxicillin-clavulanic acid
A penicillin-resistant Neisseria gonorrhoeae strand A Sus Sus
produces: stand B Sus Res
a alpha-hemolysin strand C Res Sus
b beta-lactamase strand D Res Res
c enterotoxin Based on the above results for oxacillin and
d coagulase - ANSWER -b beta-lactamase amoxicillin, which strand is heteroresistant?
a strand A
b Antimicrobial resistance in Neisseria gonorrhoeae b strand B
is widespread. The production of beta-lactamase c strand C
(penicillinase) breaks open the beta lactam ring of d strand D - ANSWER -d strand D
penicillin, destroying its activity. Thus, Ngonorrhoeae
that produce beta lactamase are resistant to d A Staphylococcus aureus isolate with an MIC of 4
penicillin. pg/mL is resistant to oxacillin.. As per the Clinical and
Laboratory Standards Institute (CLSI)
recommendations a heteroresistant strain would be
Which selective medium is used for the isolation of defined as a methicillin (oxacillin) resistant S aureus
gram-positive microorganisms? (MRSA/ORSA). An MRSA/ORSA isolate would be
a Columbia CNA with 5% sheep blood reported as resistant to all beta lactam agents, beta
b trypticase soy agar with 5% sheep blood lactam/beta lactamase inhibitor combinations, such
c eosin methylene blue as amoxicillin- clavulanic acid, and carbapenems.
d modified Thayer-Martin - ANSWER -a
Columbia CNA with 5% sheep blood
13 An Enterococcus isolated from multiple blood
a Columbia CNA agar contains colistin and nalidixic cultures in a patient endocarditis should be:
acid, which inhibit most gram-negative organisms. a screened for high level aminoglycoside resistance
Eosin methylene blue is selective and inhibits gram- b checked for tolerance
, BOC Microbiology Test Questions and Answers Rated A
c assayed for serum antimicrobial activity resistant. The Clinical Laboratory Standards Institute
d tested for beta-lactamase production - (CLSI) recommends addition of 2% NaCl, incubation
ANSWER -a screened for high level at 35±2°C, and incubation for 24 hours when
aminoglycoside resistance performing susceptibility testing of S aureus against
oxacillin.
a Systemic enterococcal infections, such as
endocarditis, are commonly treated with a cell-wall-
active agent and an aminoglycoside. When performing a stool culture, a colony type typical
These agents act synergistically to kill the organism. of an enteric pathogen is subcultured on a blood agar
plate. The resulting pure culture is screened with
If the organism is resistant to one or both, there is no
synergy, and the combination will fail. It is importantseveral tests to obtain the following results:
to detect aminoglycoside and beta-lactam resistance TSI: acid butt, alkaline slant, no gas, no H2S
in these cases. Enterococci have intrinsic moderate phenylalanine deaminase: negative motility: positive
level resistance to aminoglycosides. Acquired serological typing: Shigella flexneri (Shigella
resistance corresponds to very high MICs (greater subgroup B)
than 500 pg/mL) for gentamicin and is termed high The serological typing is verified with new kit and
level resistance. controls. The best course of action would be to:
a report the organism as Shigella flexneri without
further testing
In the Kirby-Bauer disc diffusion susceptibility test, b verify reactivity of motility medium with positive and
which variable is critical when testing Pseudomonas negative controls
species for antibiotic susceptibility to c verify reactivity of the TSI slants with
aminoglycosides? positive and negative controls for H2S
a incubation temperature production
b duration of incubation d verify reactivity of phenylalanine d
c cation content of media aminase with positive and negative controls -
d depth of agar - ANSWER -c cation content of ANSWER -b verify reactivity of motility medium
media with positive and negative controls
c Variations in the concentrations of divalent cations b All of the biochemical and serological
primarily calcium and magnesium affect the results of reactions listed are consistent with an identification of
aminoglycoside, tetracycline and colistin tests with P Shigella flexneri, with the exception of motility. All
aeruginosa isolates. A cation concentration that is Shigella are nonmotile.
too high results in smaller zone sizes, and a
concentration that is too low increases zone sizes.
Susceptibility testing performed on quality control
organisms using a new media lot number yielded
The procedure that assures the most accurate zone sizes that were too large for all antibiotics
detection of mecA-mediated oxacillin resistance in tested. The testing was repeated using media from a
routine broth microdilution susceptibility testing previously used lot number, and all zone sizes were
against S aureus is: acceptable. Which of the following best explains the
a addition of 4% NaCl unacceptable zone sizes?
b incubation at 30°C a the antibiotic disks were not stored with the proper
c incubation for 48 hours desiccant
d use of cefoxitin for testing - ANSWER -d use b the depth of the media was too thick
of cefoxitin for testing c the depth of the media was too thin
d the antibiotic disks were not properly applied to the
d Cefoxitin is used as a surrogate for mecA-mediated media - ANSWER -c the depth of the media
oxacillin resistance in S aureus. S aureus with was too thin
cefoxitin MICs >4 pg/mL are considered oxacillin
, BOC Microbiology Test Questions and Answers Rated A
c All Mueller-Hinton agar used for disk selective media is recommended for recovery from
diffusion susceptibility testing should be poured to a fecal specimens. Selective media for Campylobacter
depth of 4mm. If the depth of the media is <4mm, this contains antibiotics to inhibit the growth of enteric
may be associated with excessively large zones and gram-negative flora. Unlike other enteric pathogens,
false- positive susceptibility results. Agar that is C coli/jejuni grow well at 42°C.
>4mm in depth may cause excessively small zone
sizes.
An expectorated sputum is sent to the laboratory for
culture from a patient with respiratory distress. The
Three sets of blood cultures were obtained from an Gram stain of the specimen shows many squamous
adult patient with fever and suspected endocarditis. epithelial cells (>25/lpf) and rare neutrophils. The
The aerobic bottle of one set had growth of microscopic appearance of the organisms present
Staphylococcus epidermidis at 5 days of incubation. include:
This indicates that: moderate gram-positive cocci in chains and
a there was low-grade bacteremia diplococci moderate gram-negative diplococci
b the organism is most likely a contaminant moderate palisading gram-positive bacilli all in
c the patient has a line infection moderate amounts
d the blood culture bottles are defective - This Gram stain is most indicative of:
ANSWER -b the organism is most likely a a a pneumococcal pneumonia
contaminant b an anaerobic infection
c an Haemophilus pneumonia
b Coagulase-negative staphylococci are commonly d oropharyngeal flora - ANSWER -d
associated with contaminated blood cultures; oropharyngeal flora
however, they are also increasing as a cause of true
bacteremia. Significant bacteremia in a patient with d Sputum specimen quality is assessed to determine
endocarditis is usually continuous and low grade. In if the specimen is representative of the site of
most cases, all blood cultures drawn will yield infection. The presence of white blood cells is an
positive results. The facts that only 1 bottle of 1 set indicator of infection, and presence of squamous
was positive, and that the bottle did not become epithelial cells is an indicator of oropharyngeal
positive until day 5 of incubation, indicate that this contamination.
isolate is most likely a contaminant. In this specimen, >25 epithelial cells per low power
field is an indicator of poor specimen quality, and the
bacteria present are representative of oropharyngeal
In order to isolate Campylobacter coli/jejuni, the fecal flora.
specimen should be:
a inoculated onto selective plating media and
incubated in reduced oxygen with added CO2 at Which type of microscope would be most useful in
42°C examining viruses and the structure of microbial
b stored in tryptic soy broth before plating to ensure cells?
growth of the organism a electron
c inoculated onto selective plating media and b phase-contrast
incubated at both 35°C and at room temperature c dark-field
d incubated at 35°C for 2 hours in Cary-Blair media d bright-fleld - ANSWER -a electron
before inoculating onto selective plating media -
ANSWER -a inoculated onto selective plating a Due to the small size of viruses, they are
media and incubated in reduced oxygen with added not visible using light microscopy. Electron
CO2 at 42°C microscopy is used to visualize viruses and the
internal structure of microorganisms.
a Campylobacter coli/jejuni require a microaerophilic
atmosphere for optimal recovery. The use of
