Mycology Direct Microscopic Examination and Staining Techniques

These flashcards cover the variety of direct microscopic techniques used in mycology, including staining methods, KOH preparations, and various fungal morphological classifications.

Mycology Direct Microscopic Examination

A diagnostic procedure used for the rapid presumptive identification of fungal pathogens, particularly useful for fastidious organisms that do not grow in vitro.

Gram Stain (Fungi)

A differential staining technique where fungal elements appear Gram-positive or Gram-variable; yeasts typically appear Gram-positive while true hyphae appear Gram-negative.

Blastoconidia

Budding yeast cells, particularly when the mother cell is elongated, which form pseudohyphae and appear Gram-positive.

Pseudohyphae

A false hyphal structure formed by elongated yeast cells (blastoconidia).

Septated hyphae

Hyphal structures where each septation represents an individual cell, characteristic of multicellular molds.

Sparsely septated hyphae

Hyphae characterized by having septations located far apart.

Aseptate hyphae

Hyphae lacking cross-walls, typically observed in rhizoid groups or organisms with root-like structures.

India Ink

A negative stain used to detect the polysaccharide capsule of encapsulated fungi, creating a "clear halo" around the organism against a semi-opaque background.

Encapsulated Fungi

Fungi belonging to the genus Cryptococcus, specifically Cryptococcus neoformas and C. canii, which produce a capsule detectable by India Ink.

Negative Stain

A staining technique where the background is stained (e.g., with India Ink) while the target organism, such as a yeast cell, remains unstained.

KOH (Potassium Hydroxide)

A clearing agent that breaks down proteinaceous host components (epithelial debris and tissues) without altering the structure of fungal elements.

$10\%$ KOH

The concentration of Potassium Hydroxide used for clearing skin scrapings and other fluid or aspirated specimens.

$20\%$ KOH

The concentration of Potassium Hydroxide used for dense specimens such as nails, hair, or tissue.

Arthroconidia

Barrel-shaped spores produced directly from hyphal structures after the fragmentation of hyphae, such as those found in Microsporum gypsum.

Monomorphic

Fungi that exist in only one form, either as a yeast or as a mold.

Dimorphic

Fungi that can grow in two forms (mold or yeast) depending on temperature, typically as molds at room temperature and yeasts at $37\,^\circ\text{C}$, but not simultaneously.

Polymorphic

Fungi, such as Exofiala genselmi, that manifest both hyphal structures and yeast cells at the same time.

Calcofluor White

A fluorescent dye that targets the chitin in fungal cell walls, producing apple-green, blue-green, or electric blue fluorescence under a fluorescence microscope.

Chitin

The specific component of the fungal cell wall that Calcofluor White binds to for visualization.

Sportotrx shenkii

A dimorphic fungus that produces rosette mold forms or broad-based budding yeast forms and causes fixed cutaneous or lymph cutaneous lesions from rose thorns.