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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Dermatophytes, Sporothrix, and Other Superficial and Subcutaneous Fungi

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Dermatophytes - Mycology

Dermatophytoses are superficial infections of the skin and its appendages, commonly known as ringworm, athlete’s foot, and jock itch.

Dermatophytes

Dermatophytoses are superficial infections of the skin and its appendages, commonly known as ringworm, athlete’s foot, and jock itch. They are caused by species of the gen-era Microsporum, Trichophyton, and Epidermophyton, which are 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.

MYCOLOGY

Dermatophytes (literally, skin-plants) are molds that have been classified as Deuteromycetes (fungi imperfecti). The three genera of medical importance are Epidermo-phyton, Microsporum, and Trichophyton, which are separated primarily by the morphologyof their macroconidia and presence of microconidia. The sexual forms have been discov-ered for many of the Microsporum and Trichophytonspecies and assigned to ascomycete genera (Arthroderma, Nannizzia). 


Dermatophytes are still called by their previous names in the medical literature for reasons of familiarity and because identification procedures continue to be based on the characteristics of their conidia. Many species cause dermato-phyte infections; the most common of these are shown in Table 47–1. They require a few days to a week or more to initiate growth. Most grow best at 25°C on Sabouraud’s agar, which is usually used for culture. The hyphae are septate, and their conidia may be borne directly on the hyphae or on conidiophores. Small microconidia may or may not be formed; however, the larger and more distinctive macroconidia (Fig 47–1C) are usually the basis for identification.



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