MICROBIOLOGY AND PARASITOLOGY: A
TEXTBOOK AND LABORATORY MANUAL
FOR THE HEALTH SCIENCES
2ND EDITION
• AUTHOR(S)FE A. BARTOLOME, AND
ELIZABETH P. QUILES
TEST BANK
1)
Reference
Ch. 1 — The Science of Microbiology
Stem
A 45-year-old patient with a postoperative wound infection
yields scant white-gray colonies on blood agar after 48 hours;
Gram stain of the colony smear shows gram-positive cocci in
clusters. The lab technologist reports catalase positive and
,coagulase negative results. Which interpretation best guides the
clinician about the likely organism and next laboratory step?
Options
A. Staphylococcus aureus — report as pathogen and start
methicillin susceptibility testing.
B. Staphylococcus epidermidis — consider as possible skin
contaminant; correlate with clinical signs and repeat cultures.
C. Streptococcus pyogenes — report invasive streptococcal
infection and proceed with bacitracin testing.
D. Enterococcus faecalis — order bile esculin and salt tolerance
tests to confirm.
Correct Answer
B
Rationales
Correct (B): Gram-positive cocci in clusters that are catalase
positive and coagulase negative most closely match
Staphylococcus epidermidis, a common skin commensal and
frequent contaminant of wound cultures. The clinical
significance depends on correlation with wound appearance,
multiple positive cultures, and patient risk factors (e.g.,
prosthetic material). Repeat cultures or quantitative cultures
and clinical correlation are appropriate next steps.
Incorrect (A): S. aureus is catalase positive and coagulase
positive; coagulase negativity argues against S. aureus.
Reporting as S. aureus would risk unnecessary therapy.
Incorrect (C): S. pyogenes are gram-positive cocci in chains and
,are catalase negative, not consistent with cluster arrangement
and catalase positivity. Bacitracin testing is irrelevant here.
Incorrect (D): Enterococcus appears as gram-positive cocci in
pairs/chains and is catalase negative; bile esculin tests are used
for enterococci but the initial morphology and catalase result
do not support this organism.
Teaching Point
Catalase + / coagulase − staphylococci are often contaminants;
correlate clinically before reporting.
Citation
Bartolome, F. A., & Quiles, E. P. (Year). Microbiology and
Parasitology (2nd Ed.), Ch. 1.
2)
Reference
Ch. 1 — The Science of Microbiology
Stem
An ICU patient with fever has two blood culture sets taken. One
set grows a slow-growing, small pleomorphic gram-negative rod
that requires 48–72 hours and shows oxidase positivity. The lab
notes this organism grows poorly on MacConkey agar. Which
laboratory consideration is most appropriate for organism
identification?
Options
A. Perform oxidase and API strips; likely a non-fermenter such
, as Pseudomonas and report immediately.
B. Consider Haemophilus influenzae and subculture on
chocolate agar with factor X and V; request an additional
specimen for respiratory PCR.
C. Suspect Brucella spp.; follow biosafety protocols and notify
laboratory leadership before further workup.
D. Assume E. coli contamination; no further identification
necessary.
Correct Answer
C
Rationales
Correct (C): A slow-growing, pleomorphic gram-negative rod
that is oxidase positive and grows poorly on MacConkey could
be a fastidious or zoonotic pathogen such as Brucella or
Francisella. Brucella is hazardous to lab personnel; suspicion
requires immediate biosafety precautions and notification for
confirmatory testing in a reference lab. Safety trumps rapid
identification in this scenario.
Incorrect (A): Pseudomonas typically grows quickly and well on
MacConkey and produces oxidase positivity, but the slow
growth and poor MacConkey recovery argue against it. API
strips without biosafety consideration could endanger staff.
Incorrect (B): H. influenzae is small and fastidious but is oxidase
negative/variable and usually associated with respiratory
specimens; it requires chocolate agar with X and V factors, but
blood culture morphology plus oxidase positivity makes this less
TEXTBOOK AND LABORATORY MANUAL
FOR THE HEALTH SCIENCES
2ND EDITION
• AUTHOR(S)FE A. BARTOLOME, AND
ELIZABETH P. QUILES
TEST BANK
1)
Reference
Ch. 1 — The Science of Microbiology
Stem
A 45-year-old patient with a postoperative wound infection
yields scant white-gray colonies on blood agar after 48 hours;
Gram stain of the colony smear shows gram-positive cocci in
clusters. The lab technologist reports catalase positive and
,coagulase negative results. Which interpretation best guides the
clinician about the likely organism and next laboratory step?
Options
A. Staphylococcus aureus — report as pathogen and start
methicillin susceptibility testing.
B. Staphylococcus epidermidis — consider as possible skin
contaminant; correlate with clinical signs and repeat cultures.
C. Streptococcus pyogenes — report invasive streptococcal
infection and proceed with bacitracin testing.
D. Enterococcus faecalis — order bile esculin and salt tolerance
tests to confirm.
Correct Answer
B
Rationales
Correct (B): Gram-positive cocci in clusters that are catalase
positive and coagulase negative most closely match
Staphylococcus epidermidis, a common skin commensal and
frequent contaminant of wound cultures. The clinical
significance depends on correlation with wound appearance,
multiple positive cultures, and patient risk factors (e.g.,
prosthetic material). Repeat cultures or quantitative cultures
and clinical correlation are appropriate next steps.
Incorrect (A): S. aureus is catalase positive and coagulase
positive; coagulase negativity argues against S. aureus.
Reporting as S. aureus would risk unnecessary therapy.
Incorrect (C): S. pyogenes are gram-positive cocci in chains and
,are catalase negative, not consistent with cluster arrangement
and catalase positivity. Bacitracin testing is irrelevant here.
Incorrect (D): Enterococcus appears as gram-positive cocci in
pairs/chains and is catalase negative; bile esculin tests are used
for enterococci but the initial morphology and catalase result
do not support this organism.
Teaching Point
Catalase + / coagulase − staphylococci are often contaminants;
correlate clinically before reporting.
Citation
Bartolome, F. A., & Quiles, E. P. (Year). Microbiology and
Parasitology (2nd Ed.), Ch. 1.
2)
Reference
Ch. 1 — The Science of Microbiology
Stem
An ICU patient with fever has two blood culture sets taken. One
set grows a slow-growing, small pleomorphic gram-negative rod
that requires 48–72 hours and shows oxidase positivity. The lab
notes this organism grows poorly on MacConkey agar. Which
laboratory consideration is most appropriate for organism
identification?
Options
A. Perform oxidase and API strips; likely a non-fermenter such
, as Pseudomonas and report immediately.
B. Consider Haemophilus influenzae and subculture on
chocolate agar with factor X and V; request an additional
specimen for respiratory PCR.
C. Suspect Brucella spp.; follow biosafety protocols and notify
laboratory leadership before further workup.
D. Assume E. coli contamination; no further identification
necessary.
Correct Answer
C
Rationales
Correct (C): A slow-growing, pleomorphic gram-negative rod
that is oxidase positive and grows poorly on MacConkey could
be a fastidious or zoonotic pathogen such as Brucella or
Francisella. Brucella is hazardous to lab personnel; suspicion
requires immediate biosafety precautions and notification for
confirmatory testing in a reference lab. Safety trumps rapid
identification in this scenario.
Incorrect (A): Pseudomonas typically grows quickly and well on
MacConkey and produces oxidase positivity, but the slow
growth and poor MacConkey recovery argue against it. API
strips without biosafety consideration could endanger staff.
Incorrect (B): H. influenzae is small and fastidious but is oxidase
negative/variable and usually associated with respiratory
specimens; it requires chocolate agar with X and V factors, but
blood culture morphology plus oxidase positivity makes this less
