Exophiala dermatitidis
| Exophiala dermatitidis | |
|---|---|
| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Ascomycetes |
| Order: | Chaetothyriales |
| Family: | Herpotrichiellaceae |
| Genus: | Exophiala |
| Species: | E. dermatitidis |
| Binomial name | |
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Exophiala dermatitidis (Kano) de Hoog (1977) |
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| Synonyms | |
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Exophiala dermatitidis is a thermophilic black yeast, and a member of the Herpotrichiellaceae. While the species is only found at low abundance in nature, metabolically active strains are commonly isolated in saunas, steam baths, and dish washers.Exophiala dermatitidis only rarely causes infection in humans, however cases have been reported around the world. In East Asia, the species has caused lethal brain infections in young and otherwise healthy individuals. The fungus has been known to cause cutaneous and subcutaneous phaeohyphomycosis, and as a lung colonist in people with cystic fibrosis in Europe. In 2002, an outbreak of systemic E. dermatitidis infection occurred in women who had received contaminated steroid injections at North Carolina hospitals.
Exophiala dermatitidis forms slow growing, brown or black colonies. As is common amongst black yeasts, E. dermatitidis is an anamorphic fungus with multiple conidial forms. This morphological plasticity has complicated taxonomic determination based solely on physical appearance. Young colonies are described as waxy, mucoid, smooth, and yeastlike. Over time pigmented aerial hyphae develop, and older colonies are described as appearing filamentous and velvety.Conidia are between globular and elliptical in shape, and form at the mouth of short annellidic conidiogenous cells. Annellations can only be observed by electron microscopy. Prior to analysis by scanning electron microscope, the condiogenous cells were observed to form from non-annelated phialides and phialides without collarettes. These observations caused the species to be erroneously provided with its own monotypic genus, Wangiella. The species name Wangiella dermatitidis is still commonly used in the scientific literature.
The black fungus also takes on diverse morphologies in vivo. Infected tissues contain mixtures of ovoid yeast-like cells, short septate hyphae that may be branched or unbranched, toruloid hyphae, as well as isotopically enlarged sclerotic (muriform-like) cells that resemble those found in chromoblastomycosis. The muriform-like cells isolated from E. dermatitidis infections have thinner walls than those found in chromoblastomycosis, and cells are divided along a single plane.
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