Epidermophyton, Trichophyton, and Microsporum are considered dermatophytes.
Dermatophytes are keratinophilic, which means that they can digest keratin as a nutrient source using keratinases. This unique ability is the source of their pathogenicity. Thus, most infections are limited to superficial keratinized structures such as hair, nails, and the skin's stratum corneum (the outermost layer of the epidermis). They are uniformly resistant tocycloheximide.
The rapid diagnosis of dermatophytosis can be made with:
- a bedside potassium hydroxide prep (KOH), or
- a calcofluor white preparation of skin scrapings.
Microscopy cannot be used to distinguish among the dermatophytes; only culture can do so.
Dermatophyte infections can take many forms, including:
- tinea capitis (scalp ringworm),
- tinea corporis (ringworm),
- tinea cruris (jock itch),
- tinea pedis (athlete's foot), and
- tinea unguium (onychomycosis or toenail fungus).
