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
Q1
Reference: Ch. 1 — The Science of Microbiology
Stem: A 45-year-old patient with fever and productive cough
provides a sputum specimen. Direct light microscopy of a Gram
stain shows numerous polymorphonuclear leukocytes and
many Gram-negative coccobacilli appearing pale after
decolorization. Culture on blood agar after 24 hours yields
small, non-hemolytic colonies. Which laboratory interpretation
best explains the Gram stain and culture findings?
,A. The organism is a fastidious Gram-negative bacillus that
decolorized because cells were dead.
B. The organism is a thin-peptidoglycan Gram-positive coccus
misidentified due to over-decolorization.
C. The organism is a Gram-negative coccobacillus with
inherently weak Gram retention (e.g., Haemophilus spp.).
D. The specimen was contaminated with normal flora; findings
are not clinically significant.
Correct answer: C
Rationale — Correct (C): Haemophilus and some other small
Gram-negative coccobacilli have thin cell walls and may appear
pale after Gram decolorization; they commonly produce small,
non-hemolytic colonies on blood agar (sometimes requiring
satellite growth). The combination of many neutrophils and
consistent colony morphology supports a true pathogen rather
than contamination.
Rationale — Incorrect:
A. Dead cells may stain poorly, but abundant neutrophils and
growth of consistent colonies favor viable pathogen rather than
only dead organisms.
B. Gram-positive cocci appear purple and typically produce
different colony morphology; over-decolorization would not
explain small coccobacillary colonies.
D. Presence of numerous PMNs plus growth of consistent
colonies argues for clinical significance, not contamination.
,Teaching point: Small, weakly Gram-retaining coccobacilli cause
pale Gram stains but grow as small colonies.
Citation: Bartolome, F. A., & Quiles, E. P. (Year). Microbiology
and Parasitology. 2nd Ed., Ch. 1.
Q2
Reference: Ch. 1 — The Science of Microbiology
Stem: During an outbreak investigation in a neonatal ward,
several infants develop bloodstream infections. Environmental
swabs from a sink drain yield growth of a nonfermenting,
oxidase-positive, glucose-nonfermenting Gram-negative
bacillus. Which epidemiologic concept best links this organism
to the cluster?
A. Index case
B. Reservoir
C. Attack rate
D. Herd immunity
Correct answer: B
Rationale — Correct (B): The sink drain represents an
environmental reservoir that can harbor nonfermenting Gram-
negative bacilli (e.g., Pseudomonas or related organisms) and
serve as a persistent source for nosocomial transmission to
neonates. Identifying reservoirs is key to controlling healthcare
outbreaks.
, Rationale — Incorrect:
A. The index case is the first identified infected patient, not the
environmental source.
C. Attack rate is a measure of disease occurrence, not the
source of organisms.
D. Herd immunity is a population concept not applicable to an
environmental source in a neonatal ward.
Teaching point: Environmental reservoirs (like drains) can
sustain healthcare-associated organisms and perpetuate
outbreaks.
Citation: Bartolome, F. A., & Quiles, E. P. (Year). Microbiology
and Parasitology. 2nd Ed., Ch. 1.
Q3
Reference: Ch. 1 — The Science of Microbiology
Stem: A lab student prepares a wet mount from a stool
specimen to look for motile protozoa. Under brightfield
microscopy at 400×, she notes actively moving pear-shaped
organisms with a trailing flagellum. Which microscopic
technique and interpretation best support identification?
A. Phase-contrast microscopy will enhance contrast and help
visualize motility in live protozoa.
B. Darkfield microscopy should be used because it provides
staining for internal structures.
C. Fluorescence microscopy is required to see flagella of all
protozoa.
TEXTBOOK AND LABORATORY MANUAL
FOR THE HEALTH SCIENCES
2ND EDITION
• AUTHOR(S)FE A. BARTOLOME, AND
ELIZABETH P. QUILES
TEST BANK
Q1
Reference: Ch. 1 — The Science of Microbiology
Stem: A 45-year-old patient with fever and productive cough
provides a sputum specimen. Direct light microscopy of a Gram
stain shows numerous polymorphonuclear leukocytes and
many Gram-negative coccobacilli appearing pale after
decolorization. Culture on blood agar after 24 hours yields
small, non-hemolytic colonies. Which laboratory interpretation
best explains the Gram stain and culture findings?
,A. The organism is a fastidious Gram-negative bacillus that
decolorized because cells were dead.
B. The organism is a thin-peptidoglycan Gram-positive coccus
misidentified due to over-decolorization.
C. The organism is a Gram-negative coccobacillus with
inherently weak Gram retention (e.g., Haemophilus spp.).
D. The specimen was contaminated with normal flora; findings
are not clinically significant.
Correct answer: C
Rationale — Correct (C): Haemophilus and some other small
Gram-negative coccobacilli have thin cell walls and may appear
pale after Gram decolorization; they commonly produce small,
non-hemolytic colonies on blood agar (sometimes requiring
satellite growth). The combination of many neutrophils and
consistent colony morphology supports a true pathogen rather
than contamination.
Rationale — Incorrect:
A. Dead cells may stain poorly, but abundant neutrophils and
growth of consistent colonies favor viable pathogen rather than
only dead organisms.
B. Gram-positive cocci appear purple and typically produce
different colony morphology; over-decolorization would not
explain small coccobacillary colonies.
D. Presence of numerous PMNs plus growth of consistent
colonies argues for clinical significance, not contamination.
,Teaching point: Small, weakly Gram-retaining coccobacilli cause
pale Gram stains but grow as small colonies.
Citation: Bartolome, F. A., & Quiles, E. P. (Year). Microbiology
and Parasitology. 2nd Ed., Ch. 1.
Q2
Reference: Ch. 1 — The Science of Microbiology
Stem: During an outbreak investigation in a neonatal ward,
several infants develop bloodstream infections. Environmental
swabs from a sink drain yield growth of a nonfermenting,
oxidase-positive, glucose-nonfermenting Gram-negative
bacillus. Which epidemiologic concept best links this organism
to the cluster?
A. Index case
B. Reservoir
C. Attack rate
D. Herd immunity
Correct answer: B
Rationale — Correct (B): The sink drain represents an
environmental reservoir that can harbor nonfermenting Gram-
negative bacilli (e.g., Pseudomonas or related organisms) and
serve as a persistent source for nosocomial transmission to
neonates. Identifying reservoirs is key to controlling healthcare
outbreaks.
, Rationale — Incorrect:
A. The index case is the first identified infected patient, not the
environmental source.
C. Attack rate is a measure of disease occurrence, not the
source of organisms.
D. Herd immunity is a population concept not applicable to an
environmental source in a neonatal ward.
Teaching point: Environmental reservoirs (like drains) can
sustain healthcare-associated organisms and perpetuate
outbreaks.
Citation: Bartolome, F. A., & Quiles, E. P. (Year). Microbiology
and Parasitology. 2nd Ed., Ch. 1.
Q3
Reference: Ch. 1 — The Science of Microbiology
Stem: A lab student prepares a wet mount from a stool
specimen to look for motile protozoa. Under brightfield
microscopy at 400×, she notes actively moving pear-shaped
organisms with a trailing flagellum. Which microscopic
technique and interpretation best support identification?
A. Phase-contrast microscopy will enhance contrast and help
visualize motility in live protozoa.
B. Darkfield microscopy should be used because it provides
staining for internal structures.
C. Fluorescence microscopy is required to see flagella of all
protozoa.
