Epidermophyton, Trichophyton, and Microsporum are considered dermatophytes.
Dermatophytes are keratinophilic, which means that they are able to digest keratin as a nutrient source using keratinases. This special ability is the source of their pathogenicity, and thus, most infections are limited to superficial keratinized structures such as hair, nails, and the stratum corneum (outermost layer of the epidermis) of the skin. They are uniformly resistant to cycloheximide.
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).
