Question 1

A patient with HIV infection and a CD4+ T-cell count below 50 cells/µL develops a progressive neurological illness characterized by confusion, motor deficits, and seizures. Brain MRI reveals multiple white matter lesions without mass effect. PCR of the CSF is positive for JC virus. Thepathogenesis of this condition, progressive multifocal leukoencephalopathy (PML), involves:

Options :

A : Direct cytopathic effect of JC virus on neurons.

B : Lytic infection of oligodendrocytes by JC virus, leading to demyelination.

C : Inflammatory demyelination triggered by JC virus infection of astrocytes.

D : Opportunistic infection by JC virus due to impaired cell-mediated immunity.

Answer: B

Question 2

The human virome, the collection of viruses that reside in and on the human body, is increasinglyrecognized for its role in health and disease. Which of the following statements regarding the human virome is MOST accurate?

Options :

A : The human virome is primarily composed of pathogenic viruses that cause acute infections.

B : The composition of the human virome is relatively stable over time and is not influenced by environmental factors.

C : Bacteriophages, viruses that infect bacteria, are a significant component of the human gut virome.

D : The human virome is largely independent of the host's immune status.

Answer: C

Question 3

A microbiology laboratory is investigating an outbreak of bloodstream infections in a neonatal intensive care unit. Isolates of Staphylococcus epidermidis from multiple infants show indistinguishable banding patterns by pulsed-field gel electrophoresis (PFGE). This finding MOST strongly suggests:

Options :

A : Widespread antibiotic resistance within the S. epidermidis population.

B : A common source of infection and clonal spread of the organism.

C : Recent horizontal gene transfer of virulence factors.

D : Spontaneous mutations leading to increased pathogenicity.

Answer: B

Question 4

A microbiology laboratory is processing a stool sample for ova and parasites. A large (approximately 100 µm), thick-shelled, oval egg with a flattened side is observed. This egg MOST likely belongs to:

Options :

A : Ascaris lumbricoides

B : Enterobius vermicularis

C : Taenia species

D : Trichuris trichiura

Answer: A

Question 5

A patient develops a severe diarrheal illness after consuming raw seafood. Stool culture yields a Gramnegative, comma-shaped bacterium that is oxidase-positive and grows on thiosulfate-citrate-bile salts-sucrose (TCBS) agar, producing blue-green colonies. The MOST significant virulence factor contributing to the severe, cholera-like diarrhea caused by this organism is:

Options :

A : Heat-stable enterotoxin (ST)

B : Heat-labile toxin (LT)

C : Cholera toxin (CT)-like enterotoxin

D : Type III secretion system (T3SS)

Answer: C

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