Laboratory diagnosis of dermatophytosis (caused by Trichophyton, Microsporum, or Epidermophyton species):
Wood’s lamp examination — some Microsporum species (notably M. canis, M. audouinii) show characteristic green fluorescence of infected hair under UV light (most Trichophyton species do not fluoresce); useful for tinea capitis screening.
Direct KOH microscopy — of skin scrapings, hair, or nail clippings, demonstrating septate, branching hyphae.
Culture — on Sabouraud dextrose agar (with cycloheximide to inhibit contaminants); colony morphology, pigmentation, and microscopic conidial morphology (macroconidia/microconidia shape) allow species identification.
Specimen collection: scraping from the active, advancing edge of a skin lesion (highest fungal load); hair pluck (not just cut hair) for tinea capitis; nail clippings/subungual debris for onychomycosis.
