ASCP Microbiology 2

Question 1

Which culture medium is used for isolation of Neisseria gonorrhoeae?

Accepted Answer

Thayer-Martin agar

Answer

Modified Thayer-Martin agar contains antibiotics (vancomycin, colistin, nystatin) to select for Neisseria species from genital specimens.

Question 2

Acid-fast bacilli seen on Ziehl-Neelsen stain are most consistent with:

Accepted Answer

Mycobacterium tuberculosis

Answer

Mycobacterium tuberculosis retains carbol fuchsin after acid-alcohol decolorization due to its mycolic acid-rich cell wall.

Question 3

A positive oxidase test (purple color) differentiates which organism from Enterobacteriaceae?

Accepted Answer

Pseudomonas aeruginosa

Answer

Pseudomonas aeruginosa is oxidase-positive (contains cytochrome c oxidase), while all Enterobacteriaceae are oxidase-negative.

Question 4

Which toxin produced by Clostridium difficile causes pseudomembranous colitis?

Accepted Answer

Toxin A (enterotoxin) and Toxin B (cytotoxin)

Answer

C. difficile produces Toxin A (enterotoxin) and Toxin B (cytotoxin), both detected in stool EIA or PCR testing for diagnosis.

Question 5

India ink preparation is used to visualize the capsule of which organism in CSF?

Accepted Answer

Cryptococcus neoformans

Answer

India ink stain creates a dark background, highlighting the large capsule of Cryptococcus neoformans as a clear halo.

ASCP Practice Test