KOH CLIBAC LAB - MIDTERM REAL

Fungi classification

Eukaryotic organisms with a true nucleus

Bacteria classification

Prokaryotic organisms lacking a nucleus

Mode of reproduction of yeasts

Budding

Appearance of yeast colonies

Smooth, creamy, bacterial-like colonies without aerial hyphae

General structure of molds

Filamentous fungi forming hyphae

Mass of intertwined hyphae

Mycelium

Appearance of mold colonies

Fluffy, cottony, or powdery (fuzzy/woolly)

Primary use of KOH mount

Screening for fungal elements

Main function of KOH in KOH mount

Digests keratin and clears background tissue

What KOH mount cannot do

Identify fungal species

Best specimen for dermatophyte detection

Skin scraping from outer edge of lesion

Preparation of skin before collection

Clean with 70% alcohol

Preparation of nails before sampling

Clean with 70% alcohol then clip affected area

Hair specimen collection method

Pull 10-12 hairs with shaft using sterile forceps

Maximum length of hair specimen

Not more than 5 mm

Maximum size of skin/nail specimen

Not more than 2 mm

Main disadvantage of KOH mount

Requires experience due to confusing artifacts

Reason KOH mount may take time to clear specimen

Thick keratin requires extended digestion

Type of fungal infection affecting internal organs

Systemic mycoses

Type of fungal infection affecting keratinized tissues

Cutaneous mycoses

Type of fungal infection limited to outer skin layer

Superficial mycoses

Type of fungal infection involving deeper tissues

Subcutaneous mycoses

Causative agents of cutaneous mycoses

Dermatophytes

Microscopic finding in dermatophytes

Septate hyphae

Another possible finding depending on organism

Spherical yeast cells

Culture medium commonly used for fungi

Sabouraud Dextrose Agar (SDA)

Purpose of fungal culture

Species identification

Initial method for fungal diagnosis

Direct microscopy

Examples of direct microscopy methods

KOH mount, India ink, calcofluor white

Why KOH mount is useful

Rapid detection of fungal elements

What KOH does not dissolve

Fungal cell walls

Characteristic structure produced by molds

Hyphae

Reproductive structure seen in fungi under KOH

Conidia (spores)

Why molds appear fuzzy

Presence of aerial hyphae

Why yeasts do not appear fuzzy

Absence of aerial hyphae

Most fungi oxygen requirement

Obligate aerobes

Habitat of most fungi

Environment

Key difference between yeasts and molds

Unicellular vs filamentous structure