Mycology & Fungal Diagnostics Flashcards

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

Answer: Calcofluor white

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.

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

Answer: Candida albicans

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.

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

Answer: India ink preparation

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.

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

Answer: Sabouraud dextrose agar

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

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

Answer: Yeast cells

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.

What is the primary virulence factor of Cryptococcus neoformans that enables it to evade phagocytosis?

Answer: Polysaccharide capsule

The polysaccharide capsule (composed mainly of glucuronoxylomannan) is the primary virulence factor of Cryptococcus neoformans, inhibiting phagocytosis, complement activation, and antigen presentation.

Dermatophytes are distinguished from other fungi by their primary ability to infect which tissue types?

Answer: Keratinized tissues including skin, hair, and nails

Dermatophytes (Trichophyton, Microsporum, Epidermophyton) produce keratinases enabling colonization and infection of keratinized structures such as skin, hair, and nails, but they do not invade deeper tissues.