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Epidermophyton is a filamentous fungus and one of the three fungal genera classified as dermatophytes. It is distributed worldwide. Man is the primary host of Epidermophyton floccosum, the only species which is pathogenic. The natural habitat of the related but the nonpathogenic species Epidermophyton stockdaleae is soil [529, 1295, 2202].
The genus Epidermophyton contains two species; Epidermophyton floccosum and Epidermophyton stockdaleae. E. stockdaleae is known to be nonpathogenic, leaving E. floccosum as the only species causing infections in humans.
E. floccosum is one of the common causes of dermatophytosis in otherwise healthy individuals. It infects skin (tinea corporis, tinea cruris, tinea pedis) and nails (onychomycosis). The infection is restricted to the nonliving cornified layers of epidermis since the fungus lacks the ability to penetrate the viable tissues of the immunocompetent host [57, 1679, 2400]. Disseminated infections due to any of the dermatophytes are very unlikely due to the restriction of the infection to keratinized tissues. However, invasive E. floccosum infection has been reported in an immunocompromised patient with Behcet's syndrome . As with all forms of dermatophytosis, Epidermophyton floccosum infections are communicable and usually transmitted by contact, particularly in common showers and gym facilities.
The colonies of E. floccosum grow moderately rapidly and mature within 10 days. Following incubation at 25 °C on potato dextrose agar, the colonies are brownish yellow to olive gray or khaki from the front. From the reverse, they are orange to brown with an occasional yellow border. The texture is flat and grainy initially and become radially grooved and velvety by aging. The colonies quickly become downy and sterile [531, 1295, 2144, 2202].
Septate, hyaline hyphae, macroconidia, and occasionally, chlamydoconidium-like cells are visualized. Microconidia are typically absent. Macroconidia (10-40 x 6-12 µm) are thin walled, 3- to 5- celled, smooth, and clavate-shaped with rounded ends. They are found singly or in clusters. Chlamydoconidium-like cells, as well as arthroconidia, are common in older cultures [531, 1295, 2144, 2202].
See our histopathology page.
Microsporum and Trichophyton
Epidermophyton floccosum is differentiated from Microsporum and Trichophyton by the absence of microconidia.
It is differentiated from E. stockdaleae by the aid of some microscopic and physiological features. In contrast to E. stockdaleae, E. floccosum is frequently unable to perforate hair. Macroconidia of E. stockdaleae are longer than those of E. floccosum. In contrast to E. floccosum, E. stockdaleae is tolerant to 7% NaCl.
No special precautions other than general laboratory precautions are required.
As with the other dermatophytes, in vitro antifungal susceptibility testing methods have not been standardized for E. floccosum. However, there are some reports on in vitro activity of various antifungal drugs. Most of these studies have used the modifications of the NCCLS M 38P methodology documented for conidium forming filamentous fungi . The results of these studies show that, terbinafine, itraconazole,voriconazole, and ketoconazole generate low MICs and appear active in vitro against E. floccosum. Griseofulvin is less active than these compounds. Among all, fluconazole generates the highest MICs and appears to have the lowest activity [1119, 2307, 2310, 2432]. Amorolfine  and naftifine [1399, 2307, 2310] also exhibit in vitro activity against E. floccosum.
For MICs of various antifungal drugs for E. floccosum, see our susceptibility database.
Terbinafine, itraconazole, and ketoconazole are in common use for current treatment of E. floccosum infections [293, 548, 1003, 2205, 2281].
Onychomycosis due to Epidermophyton floccosum
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