(described by Fonseca and de Area Leao in 1928)
Taxonomic classification
Kingdom: Fungi
Phylum: Ascomycota
Class: Euascomycetes
Order: Dothideales
Family: Piedraiaceae
Genus: Piedraia
Description and Natural Habitats
Piedraia is a dematiaceous filamentous fungus found in soil particularly at tropical areas. It is one of the keratinolytic fungi and is the causative agent of black piedra in man [531, 1295].
Species
The genus Piedraia contains two species: Piedraia hortae and Piedraia quintanilhae. Piedraia hortae is the causative agent of black piedra. On the other hand, Piedraia quintanilhae has been isolated from chimpanzees in Central Africa but not much else is know about it as a pathogen. Piedraia quintanilhae differs from Piedraia hortae morphologically in that its ascospores do not have appendages [531]. On this page, we only discuss Piedraia hortae.
Pathogenicity and Clinical Significance
Piedraia hortae causes black piedra. This disease is characterized by formation of brown to black nodules that are very firmly attached to the hair shaft. The nodules are composed of ascostromata which are the fruiting body of the fungus containing asci and ascospores. Scalp hair is the most frequently infected area. Most of the cases are asymptomatic and may remain so for years. However, breaks due to weakness of the hair shaft may occur eventually in severe cases. The infection mostly involves individuals who live in tropical areas (particularly in South America) and use oily substances for hair care. Mixed infections with Piedraia hortae and Trichosporon spp. may occur [7, 459, 531, 842, 2311].
Macroscopic Features
Colonies of Piedraia hortae are slow growing, small, folded, velvety and dark brown to black in color. They may remain glabrous or covered with short aerial hyphae. Piedraia hortae may produce a reddish brown diffusable pigment. From the reverse, the colony is black in color [531] [1295].
Microscopic Features
Septate hyphae, ascostromata, asci, and ascospores are visualized. Hyphae are darkly pigmented and contain numerous intercalary chlamydoconidium-like cells. Ascostromata are pseudoparenchymatous structures which are subglobose to irregular in shape and black in color. Each usually contains a single ascus. Asci are ellipsoid, solitary or in clusters and contain 8 ascospores. Ascus walls dissolve readily. Ascospores are hyaline to darkly pigmented. They are one-celled, fusoid, curved, and taper towards both ends to form the typical whip-like appendages [531] [1295].
Laboratory Precautions
No special precautions other than general laboratory precautions are required.
Susceptibility
Very few data are available and there is as yet no standard method for in vitro susceptibility testing of Piedraia spp. Terbinafine appears active in vitro against Piedraia hortae[842, 2308].
Shaving of affected hair, topical salycylic acid, formaldehyde or azole creams are currently applied for treatment of black piedra. Oral ketoconazole or terbinafine may also be used. Relapses may occur even after appropriate management of the infection with antifungal agents [462, 842].