FORTIS MICROBIOLOGY FINAL EXAM QUESTIONS
AND ANSWERS A+ GRADED WITH EXPERT
SOLUTIONS - 150 Questions with Answers
Page 1
,Q1. In a clinical isolate of Klebsiella pneumoniae, a novel plasmid confers resistance
to carbapenems. Which molecular mechanism is most likely responsible for the
horizontal transfer of this resistance to other Enterobacteriaceae?
A. Conjugation via a type IV secretion system
B. Transduction by a lytic bacteriophage
C. Transformation with naked DNA from lysed cells
D. Site-specific recombination of an integron
Correct Answer: A. Conjugation via a type IV secretion system
Rationale: Plasmid-mediated carbapenem resistance (e.g., NDM, KPC) spreads primarily
by conjugation, a process requiring a type IV secretion system to transfer DNA between
bacteria. Transduction involves phages, transformation requires competent cells, and
integrons are gene capture systems, not transfer mechanisms.
Why Wrong:
B - Transduction is phage-mediated and not the primary mechanism for plasmid
spread.
C - Transformation is inefficient for large plasmids and not the main route in
Enterobacteriaceae.
D - Integrons capture gene cassettes but do not mediate plasmid transfer.
Reference: Murray, P.R., Rosenthal, K.S., & Pfaller, M.A. (2020). Medical Microbiology,
9th Ed., Ch. 8.
Q2. Which of the following best explains the ability of Mycobacterium tuberculosis to
persist in a latent state within granulomas despite an active immune response?
A. Expression of mycolic acids that resist lysosomal degradation
B. Inhibition of phagolysosome fusion and acidification
C. Secretion of superoxide dismutase to neutralize oxidative burst
D. Induction of host cell apoptosis to avoid immune detection
Correct Answer: B. Inhibition of phagolysosome fusion and acidification
Rationale: M. tuberculosis blocks phagolysosome fusion via the secretion of virulence
factors like PknG and SapM, allowing it to survive within macrophages. Mycolic acids
provide a permeability barrier but are not the primary persistence mechanism. SOD
neutralizes ROS but does not explain latency. Apoptosis would reduce bacterial survival.
Why Wrong:
A - Mycolic acids contribute to resistance but not specifically to phagolysosome
arrest.
C - SOD protects against oxidative stress but does not prevent phagolysosome fusion.
D - Apoptosis is a host defense that would limit bacterial persistence.
Reference: Kumar, V., Abbas, A.K., & Aster, J.C. (2020). Robbins & Cotran Pathologic
Basis of Disease, 10th Ed., Ch. 8.
Page 2
,Q3. A novel enveloped virus is found to bud from the plasma membrane of infected
cells. Which component of the viral envelope is most likely host-derived and critical
for viral entry?
A. Lipid bilayer containing host cholesterol and sphingolipids
B. Viral glycoproteins that bind host receptors
C. Host membrane proteins incorporated during budding
D. Matrix proteins that stabilize the envelope
Correct Answer: A. Lipid bilayer containing host cholesterol and sphingolipids
Rationale: The lipid bilayer of enveloped viruses is derived from host cell membranes and
contains host lipids such as cholesterol and sphingolipids, which are essential for
membrane fusion and stability. Viral glycoproteins are virus-encoded, not host-derived.
Host membrane proteins may be incorporated but are not critical for entry. Matrix
proteins are internal, not envelope components.
Why Wrong:
B - Glycoproteins are virus-encoded, not host-derived.
C - Host proteins are present but not typically required for entry.
D - Matrix proteins are not part of the lipid envelope.
Reference: Flint, S.J., Racaniello, V.R., Rall, G.F., et al. (2020). Principles of Virology, 5th
Ed., Vol. I, Ch. 3.
Q4. Which of the following best describes the mechanism of action of the antifungal
drug caspofungin?
A. Inhibition of ergosterol biosynthesis
B. Inhibition of -(1,3)-D-glucan synthase
C. Disruption of fungal cell membrane permeability
D. Inhibition of fungal DNA synthesis
Correct Answer: B. Inhibition of -(1,3)-D-glucan synthase
Rationale: Caspofungin is an echinocandin that inhibits ²-(1,3)-D-glucan synthase, an
enzyme critical for fungal cell wall integrity. This leads to osmotic instability and cell
death. Azoles inhibit ergosterol synthesis, polyenes disrupt membrane permeability, and
flucytosine inhibits DNA synthesis.
Why Wrong:
A - Ergosterol synthesis inhibition is the mechanism of azoles, not echinocandins.
C - Membrane disruption is the mechanism of polyenes like amphotericin B.
D - DNA synthesis inhibition is the mechanism of flucytosine.
Reference: Katzung, B.G., & Vanderah, T.W. (2021). Basic & Clinical Pharmacology, 15th
Ed., Ch. 48.
Page 3
, Q5. Which of the following is a major mechanism by which Plasmodium falciparum
evades host immunity?
A. Antigenic variation of surface proteins
B. Sequestration in deep vascular beds via PfEMP1
C. Production of IgA protease to degrade antibodies
D. Intracellular survival within macrophages
Correct Answer: A. Antigenic variation of surface proteins
Rationale: P. falciparum undergoes antigenic variation by switching expression of var
genes encoding PfEMP1 on infected erythrocytes, allowing it to evade antibody responses.
Sequestration is a consequence of PfEMP1 binding, not a separate evasion mechanism.
IgA protease is used by bacteria, not Plasmodium. The parasite resides in erythrocytes and
hepatocytes, not macrophages.
Why Wrong:
B - Sequestration is a result of antigenic variation and not an independent evasion
mechanism.
C - IgA protease is not produced by Plasmodium.
D - Plasmodium does not primarily survive in macrophages.
Reference: Murray, P.R., Rosenthal, K.S., & Pfaller, M.A. (2020). Medical Microbiology,
9th Ed., Ch. 84.
Q6. Which of the following is the most appropriate method to differentiate between
Clostridioides difficile infection and colonization in a patient with diarrhea?
A. Detection of glutamate dehydrogenase (GDH) antigen in stool
B. Nucleic acid amplification test (NAAT) for toxin genes
C. Stool culture on selective media
D. Enzyme immunoassay (EIA) for toxins A and B
Correct Answer: D. Enzyme immunoassay (EIA) for toxins A and B
Rationale: EIA for toxins A and B detects the actual toxins, which are responsible for
disease, thus differentiating infection (toxin present) from colonization (toxin absent).
NAAT detects toxin genes, which can be present in colonized individuals. GDH antigen
indicates the presence of the organism but not toxin production. Stool culture also cannot
distinguish toxigenic from non-toxigenic strains without further testing.
Why Wrong:
A - GDH antigen only indicates the presence of the organism, not toxin production.
B - NAAT detects toxin genes, which may be present in asymptomatic colonization.
C - Stool culture requires further testing to determine toxigenicity.
Reference: McDonald, L.C., et al. (2018). Clinical Practice Guidelines for Clostridium
difficile Infection in Adults and Children: 2017 Update by the IDSA/SHEA.
Clinical Infectious Diseases, 66(7), e1-e48.
Page 4
AND ANSWERS A+ GRADED WITH EXPERT
SOLUTIONS - 150 Questions with Answers
Page 1
,Q1. In a clinical isolate of Klebsiella pneumoniae, a novel plasmid confers resistance
to carbapenems. Which molecular mechanism is most likely responsible for the
horizontal transfer of this resistance to other Enterobacteriaceae?
A. Conjugation via a type IV secretion system
B. Transduction by a lytic bacteriophage
C. Transformation with naked DNA from lysed cells
D. Site-specific recombination of an integron
Correct Answer: A. Conjugation via a type IV secretion system
Rationale: Plasmid-mediated carbapenem resistance (e.g., NDM, KPC) spreads primarily
by conjugation, a process requiring a type IV secretion system to transfer DNA between
bacteria. Transduction involves phages, transformation requires competent cells, and
integrons are gene capture systems, not transfer mechanisms.
Why Wrong:
B - Transduction is phage-mediated and not the primary mechanism for plasmid
spread.
C - Transformation is inefficient for large plasmids and not the main route in
Enterobacteriaceae.
D - Integrons capture gene cassettes but do not mediate plasmid transfer.
Reference: Murray, P.R., Rosenthal, K.S., & Pfaller, M.A. (2020). Medical Microbiology,
9th Ed., Ch. 8.
Q2. Which of the following best explains the ability of Mycobacterium tuberculosis to
persist in a latent state within granulomas despite an active immune response?
A. Expression of mycolic acids that resist lysosomal degradation
B. Inhibition of phagolysosome fusion and acidification
C. Secretion of superoxide dismutase to neutralize oxidative burst
D. Induction of host cell apoptosis to avoid immune detection
Correct Answer: B. Inhibition of phagolysosome fusion and acidification
Rationale: M. tuberculosis blocks phagolysosome fusion via the secretion of virulence
factors like PknG and SapM, allowing it to survive within macrophages. Mycolic acids
provide a permeability barrier but are not the primary persistence mechanism. SOD
neutralizes ROS but does not explain latency. Apoptosis would reduce bacterial survival.
Why Wrong:
A - Mycolic acids contribute to resistance but not specifically to phagolysosome
arrest.
C - SOD protects against oxidative stress but does not prevent phagolysosome fusion.
D - Apoptosis is a host defense that would limit bacterial persistence.
Reference: Kumar, V., Abbas, A.K., & Aster, J.C. (2020). Robbins & Cotran Pathologic
Basis of Disease, 10th Ed., Ch. 8.
Page 2
,Q3. A novel enveloped virus is found to bud from the plasma membrane of infected
cells. Which component of the viral envelope is most likely host-derived and critical
for viral entry?
A. Lipid bilayer containing host cholesterol and sphingolipids
B. Viral glycoproteins that bind host receptors
C. Host membrane proteins incorporated during budding
D. Matrix proteins that stabilize the envelope
Correct Answer: A. Lipid bilayer containing host cholesterol and sphingolipids
Rationale: The lipid bilayer of enveloped viruses is derived from host cell membranes and
contains host lipids such as cholesterol and sphingolipids, which are essential for
membrane fusion and stability. Viral glycoproteins are virus-encoded, not host-derived.
Host membrane proteins may be incorporated but are not critical for entry. Matrix
proteins are internal, not envelope components.
Why Wrong:
B - Glycoproteins are virus-encoded, not host-derived.
C - Host proteins are present but not typically required for entry.
D - Matrix proteins are not part of the lipid envelope.
Reference: Flint, S.J., Racaniello, V.R., Rall, G.F., et al. (2020). Principles of Virology, 5th
Ed., Vol. I, Ch. 3.
Q4. Which of the following best describes the mechanism of action of the antifungal
drug caspofungin?
A. Inhibition of ergosterol biosynthesis
B. Inhibition of -(1,3)-D-glucan synthase
C. Disruption of fungal cell membrane permeability
D. Inhibition of fungal DNA synthesis
Correct Answer: B. Inhibition of -(1,3)-D-glucan synthase
Rationale: Caspofungin is an echinocandin that inhibits ²-(1,3)-D-glucan synthase, an
enzyme critical for fungal cell wall integrity. This leads to osmotic instability and cell
death. Azoles inhibit ergosterol synthesis, polyenes disrupt membrane permeability, and
flucytosine inhibits DNA synthesis.
Why Wrong:
A - Ergosterol synthesis inhibition is the mechanism of azoles, not echinocandins.
C - Membrane disruption is the mechanism of polyenes like amphotericin B.
D - DNA synthesis inhibition is the mechanism of flucytosine.
Reference: Katzung, B.G., & Vanderah, T.W. (2021). Basic & Clinical Pharmacology, 15th
Ed., Ch. 48.
Page 3
, Q5. Which of the following is a major mechanism by which Plasmodium falciparum
evades host immunity?
A. Antigenic variation of surface proteins
B. Sequestration in deep vascular beds via PfEMP1
C. Production of IgA protease to degrade antibodies
D. Intracellular survival within macrophages
Correct Answer: A. Antigenic variation of surface proteins
Rationale: P. falciparum undergoes antigenic variation by switching expression of var
genes encoding PfEMP1 on infected erythrocytes, allowing it to evade antibody responses.
Sequestration is a consequence of PfEMP1 binding, not a separate evasion mechanism.
IgA protease is used by bacteria, not Plasmodium. The parasite resides in erythrocytes and
hepatocytes, not macrophages.
Why Wrong:
B - Sequestration is a result of antigenic variation and not an independent evasion
mechanism.
C - IgA protease is not produced by Plasmodium.
D - Plasmodium does not primarily survive in macrophages.
Reference: Murray, P.R., Rosenthal, K.S., & Pfaller, M.A. (2020). Medical Microbiology,
9th Ed., Ch. 84.
Q6. Which of the following is the most appropriate method to differentiate between
Clostridioides difficile infection and colonization in a patient with diarrhea?
A. Detection of glutamate dehydrogenase (GDH) antigen in stool
B. Nucleic acid amplification test (NAAT) for toxin genes
C. Stool culture on selective media
D. Enzyme immunoassay (EIA) for toxins A and B
Correct Answer: D. Enzyme immunoassay (EIA) for toxins A and B
Rationale: EIA for toxins A and B detects the actual toxins, which are responsible for
disease, thus differentiating infection (toxin present) from colonization (toxin absent).
NAAT detects toxin genes, which can be present in colonized individuals. GDH antigen
indicates the presence of the organism but not toxin production. Stool culture also cannot
distinguish toxigenic from non-toxigenic strains without further testing.
Why Wrong:
A - GDH antigen only indicates the presence of the organism, not toxin production.
B - NAAT detects toxin genes, which may be present in asymptomatic colonization.
C - Stool culture requires further testing to determine toxigenicity.
Reference: McDonald, L.C., et al. (2018). Clinical Practice Guidelines for Clostridium
difficile Infection in Adults and Children: 2017 Update by the IDSA/SHEA.
Clinical Infectious Diseases, 66(7), e1-e48.
Page 4
