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The least invasive of pathogenic fungi are the dermatophytes and other superficial fungi that are adapted to the keratinized outer layers of the skin. The subcutaneous fungi go a step farther by extending to the tissue beneath the skin but rarely invade deeper. Both are discussed here and summarized in Table 45–1.
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Dermatophytoses are superficial infections of the skin and its appendages, commonly known as ringworm (Figure 45–1), athlete's foot, and jock itch. They are caused by species of three genera collectively known as dermatophytes. These fungi are highly adapted to the nonliving, keratinized tissues of nails, hair, and the stratum corneum of the skin. The source of infection may be humans, animals, or the soil.
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The three genera of medically important dermatophytes (literally, skin-plants) are Epidermophyton, Microsporum, and Trichophyton. They are separated primarily by the morphology of their macroconidia and the presence of microconidia. Many species cause dermatophyte infections; the most common of these are listed in Table 45–1. They require a few days to a week or more to initiate growth. Most grow best at ...