SM Mycology & Fungal Diagnostics

Question 1

Which stain is most commonly used for the direct microscopic detection of fungi in clinical specimens due to its ability to bind chitin?

Accepted Answer

Calcofluor white

Answer

Calcofluor white binds to chitin in fungal cell walls and fluoresces brightly under UV light, making it highly sensitive for detecting fungi directly in clinical specimens.

Question 2

Which Candida species produces a germ tube when incubated in serum at 37°C for 2–3 hours?

Accepted Answer

Candida albicans

Answer

Candida albicans (and C. dubliniensis) produces germ tubes — true hyphal extensions without a constriction at the origin — when incubated in serum at 37°C, enabling rapid presumptive identification.

Question 3

Which preparation is used to visualize the characteristic polysaccharide capsule of Cryptococcus neoformans in CSF?

Accepted Answer

India ink preparation

Answer

India ink preparation creates a negative stain in which the large polysaccharide capsule of Cryptococcus neoformans appears as a clear halo surrounding the yeast cell against the dark background.

Question 4

Which culture medium is the standard primary isolation medium for fungi in clinical laboratories due to its selective acidic pH?

Accepted Answer

Sabouraud dextrose agar

Answer

Sabouraud dextrose agar (pH 5.6) selectively supports fungal growth while inhibiting most bacteria due to its acidic pH and high glucose concentration.

Question 5

Histoplasma capsulatum, a thermally dimorphic fungus, converts to which morphological form at 37°C (human body temperature)?

Accepted Answer

Yeast cells

Answer

Thermally dimorphic fungi such as Histoplasma capsulatum convert from mold (room temperature, 25–30°C) to yeast form at body temperature (37°C), which is the tissue-invasive phase.

(SM) Specialist in Microbiology Practice Test

(SM) Specialist in Microbiology Practice Test

SM Mycology & Fungal Diagnostics