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 lab technologist is preparing to examine a Gram-
stained smear from a patient’s sputum for small rod-shaped
bacteria. Under the light microscope the 40× objective shows
low detail and the 100× objective is labeled "oil". Which choice
best explains why the technologist should use the 100× oil-
immersion objective to evaluate fine bacterial morphology?
A. The oil-immersion objective increases total magnification
,above 1000×, which is required to visualize bacteria.
B. Immersion oil increases numerical aperture and resolution,
reducing light refraction and improving detail at high
magnification.
C. The oil prevents bacterial cells from moving on the slide so
morphology is preserved.
D. Oil-immersion changes refractive index to render Gram-
negative bacteria purple.
Correct Answer: B
Rationales
Correct (B): Immersion oil bridges the gap between the glass
slide and the 100× objective, increasing the numerical aperture
and minimizing refraction; this improves resolving power so fine
bacterial shapes and arrangements are distinguishable.
A: Total magnification alone doesn't determine resolution;
magnification without sufficient numerical aperture yields a
larger but blurry image.
C: Oil does not immobilize cells — fixation and heat/chemical
fixation preserve morphology.
D: Oil does not alter staining chemistry; it affects optics, not
Gram reaction.
Teaching point: Use 100× oil to maximize resolution by
increasing numerical aperture.
Citation: Bartolome, F. A., & Quiles, E. P. (Year). Microbiology
and Parasitology. 2nd Ed., Ch. 1.
,2)
Reference: Ch. 1 — The Science of Microbiology
Stem: A hospital must sterilize a heat-sensitive enzyme solution
before adding it to culture media. Autoclaving would denature
the enzyme. Which method is most appropriate to sterilize the
solution while preserving enzyme activity?
A. Autoclave at 121°C for 15 minutes.
B. Boil the solution for 30 minutes.
C. Filter-sterilize through a 0.22 µm membrane into a sterile
container.
D. Expose the solution to UV light for 60 minutes.
Correct Answer: C
Rationales
Correct (C): Membrane (0.22 µm) filtration physically removes
bacteria and many other microorganisms without heat,
preserving heat-labile enzymes and proteins.
A: Autoclaving denatures proteins and inactivates enzymes.
B: Boiling does not reliably sterilize and will also denature
sensitive proteins.
D: UV irradiation has limited penetration and is not reliable for
sterilizing liquids; it may not inactivate all microbes in solution
and can damage proteins.
Teaching point: Use 0.22 µm membrane filtration to sterilize
heat-labile solutions.
Citation: Bartolome, F. A., & Quiles, E. P. (Year). Microbiology
and Parasitology. 2nd Ed., Ch. 1.
, 3)
Reference: Ch. 1 — The Science of Microbiology
Stem: A phlebotomist collects blood for culture. The first bottle
yields skin contaminants (coagulase-negative staphylococci)
while subsequent sets grow a Gram-positive cocci in chains; the
patient has fever, IV line, and signs of sepsis. Which
interpretation and action is most appropriate?
A. Discard all culture results; contamination is certain because
skin flora was found.
B. Treat the first bottle growth as contamination, but consider
later positive sets with clinical signs as true bacteremia and
notify clinician.
C. Assume all isolates are the same contaminant and no
treatment is needed.
D. Report the culture negative because contaminants invalidate
the test.
Correct Answer: B
Rationales
Correct (B): Single-bottle skin contaminants are common;
however growth of a consistent organism (Gram-positive cocci
in chains — e.g., Streptococcus species) in multiple blood
culture sets combined with clinical sepsis suggests true
bacteremia that should be reported and acted on.
A: Discarding all results risks missing true infection; not
appropriate when clinical correlation supports infection.
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 lab technologist is preparing to examine a Gram-
stained smear from a patient’s sputum for small rod-shaped
bacteria. Under the light microscope the 40× objective shows
low detail and the 100× objective is labeled "oil". Which choice
best explains why the technologist should use the 100× oil-
immersion objective to evaluate fine bacterial morphology?
A. The oil-immersion objective increases total magnification
,above 1000×, which is required to visualize bacteria.
B. Immersion oil increases numerical aperture and resolution,
reducing light refraction and improving detail at high
magnification.
C. The oil prevents bacterial cells from moving on the slide so
morphology is preserved.
D. Oil-immersion changes refractive index to render Gram-
negative bacteria purple.
Correct Answer: B
Rationales
Correct (B): Immersion oil bridges the gap between the glass
slide and the 100× objective, increasing the numerical aperture
and minimizing refraction; this improves resolving power so fine
bacterial shapes and arrangements are distinguishable.
A: Total magnification alone doesn't determine resolution;
magnification without sufficient numerical aperture yields a
larger but blurry image.
C: Oil does not immobilize cells — fixation and heat/chemical
fixation preserve morphology.
D: Oil does not alter staining chemistry; it affects optics, not
Gram reaction.
Teaching point: Use 100× oil to maximize resolution by
increasing numerical aperture.
Citation: Bartolome, F. A., & Quiles, E. P. (Year). Microbiology
and Parasitology. 2nd Ed., Ch. 1.
,2)
Reference: Ch. 1 — The Science of Microbiology
Stem: A hospital must sterilize a heat-sensitive enzyme solution
before adding it to culture media. Autoclaving would denature
the enzyme. Which method is most appropriate to sterilize the
solution while preserving enzyme activity?
A. Autoclave at 121°C for 15 minutes.
B. Boil the solution for 30 minutes.
C. Filter-sterilize through a 0.22 µm membrane into a sterile
container.
D. Expose the solution to UV light for 60 minutes.
Correct Answer: C
Rationales
Correct (C): Membrane (0.22 µm) filtration physically removes
bacteria and many other microorganisms without heat,
preserving heat-labile enzymes and proteins.
A: Autoclaving denatures proteins and inactivates enzymes.
B: Boiling does not reliably sterilize and will also denature
sensitive proteins.
D: UV irradiation has limited penetration and is not reliable for
sterilizing liquids; it may not inactivate all microbes in solution
and can damage proteins.
Teaching point: Use 0.22 µm membrane filtration to sterilize
heat-labile solutions.
Citation: Bartolome, F. A., & Quiles, E. P. (Year). Microbiology
and Parasitology. 2nd Ed., Ch. 1.
, 3)
Reference: Ch. 1 — The Science of Microbiology
Stem: A phlebotomist collects blood for culture. The first bottle
yields skin contaminants (coagulase-negative staphylococci)
while subsequent sets grow a Gram-positive cocci in chains; the
patient has fever, IV line, and signs of sepsis. Which
interpretation and action is most appropriate?
A. Discard all culture results; contamination is certain because
skin flora was found.
B. Treat the first bottle growth as contamination, but consider
later positive sets with clinical signs as true bacteremia and
notify clinician.
C. Assume all isolates are the same contaminant and no
treatment is needed.
D. Report the culture negative because contaminants invalidate
the test.
Correct Answer: B
Rationales
Correct (B): Single-bottle skin contaminants are common;
however growth of a consistent organism (Gram-positive cocci
in chains — e.g., Streptococcus species) in multiple blood
culture sets combined with clinical sepsis suggests true
bacteremia that should be reported and acted on.
A: Discarding all results risks missing true infection; not
appropriate when clinical correlation supports infection.
