Question 1

A clinical microbiology laboratory is using flow cytometry to analyze lymphocyte subsets in a patient with suspected immunodeficiency. Which of the following cell surface markers is typically used to identify helper T cells?

Options :

A : CD8

B : CD4

C : CD19

D : CD56

Answer: B

Question 2

A research laboratory is investigating the mechanisms of viral latency in herpes simplex virus type 1 (HSV1). During latency in sensory neurons, the viral genome exists as a circular episome. Whichof the following viral gene products is thought to play a crucial role in maintaining this latent state and preventing viral gene expression?

Options :

A : Immediate-early (IE) proteins such as ICP4 and ICP27.

B : Early (E) proteins such as thymidine kinase and DNA polymerase.

C : Late (L) proteins such as structural glycoproteins.

D : Latency-associated transcripts (LATs).

Answer: D

Question 3

A clinical laboratory performs a cefoxitin disk diffusion test on a Staphylococcus aureus isolate from a wound culture. The zone of inhibition measures 18 mm. According to current CLSI M100 guidelines, how should this result be interpreted regarding oxacillin/methicillin susceptibility?

Options :

A : Susceptible (report oxacillin as susceptible)

B : Resistant (report oxacillin as resistant; infer MRSA)

C : Intermediate (requires MIC testing)

D : Indeterminate (requires mecA gene testing)

Answer: B

Question 4

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 5

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

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