Question 1

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 2

Metagenomic analysis of a bronchoalveolar lavage (BAL) sample from a patient with severe pneumonia reveals a complex microbial community with a high abundance of both bacterial and fungal sequences. This approach is particularly useful in identifying:

Options :

A : The specific antibiotic susceptibility profile of the predominant bacterial pathogen.

B : The presence of fastidious or unculturable pathogens that may be missed by traditional methods.

C : The relative proportions of different immune cell populations in the BAL fluid.

D : The presence of specific virulence factors expressed by the identified pathogens.

Answer: B

Question 3

An acid-fast bacillus isolate recovered from a respiratory specimen after 3 weeks of incubation on LöwensteinJensen medium is initially non-pigmented when grown in the dark. After exposure to light for several hours, the colonies develop a distinct yellow-orange pigment. This organism is classified as a:

Options :

A : Scotochromogen

B : Photochromogen

C : Nonchromogen

D : Rapid grower

Answer: B

Question 4

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 5

Which biosafety level (BSL) is required for clinical laboratory work involving the propagation (culture) of Coccidioides immitis/posadasii?

Options :

A : BSL-1

B : BSL-2

C : BSL-3

D : BSL-4

Answer: C

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