Question
Dermatophytes
Answer
Dermatophytes are a group of closely related keratinophilic fungi — genera Trichophyton, Microsporum, and Epidermophyton — that specifically infect keratinized tissue (skin, hair, nails), collectively causing dermatophytoses (tinea/ringworm infections).
Classification by habitat: anthropophilic (human-adapted, e.g., T. rubrum); zoophilic (animal-adapted, e.g., M. canis from cats/dogs); geophilic (soil-dwelling, e.g., M. gypseum).
Clinical patterns: tinea capitis (scalp), tinea corporis (body — annular lesion with central clearing and active advancing edge), tinea cruris (groin), tinea pedis (feet), tinea unguium/onychomycosis (nails).
Laboratory diagnosis: Wood’s lamp examination (some Microsporum species fluoresce green); direct KOH microscopy of scrapings showing septate, branching hyphae; culture on Sabouraud dextrose agar for species identification via colony/conidial morphology.
Treatment: topical antifungals for limited disease; oral antifungals (terbinafine, itraconazole, griseofulvin) for extensive disease, tinea capitis, or onychomycosis.