Ultrastructural aspect of the keratinolytic activity of piedra.

Piedra are considered asymptomatic superficial mycoses characterised by fungal growth that form nodules on the outside of hair shaft. Two types of piedra exist: white piedra (trichosporosis) caused by the basidiomycetous yeasts Trichosporon spp. and black piedra produced by the ascomycete Piedraia hortae. While the first produce soft white or light brown nodules formed by closely attached fungal elements (hyphae and arthroconidia), the second produce hard black nodules formed by a compact fungal stroma within which asci and ascospores originated. Nodules of white piedra are less fixed on hair than those of the black variety and can easily be removed. Classically it has been considered that, although neither fungal infection generally alters or destroys the keratin of hair cortex, they both disrupt the hair cuticle. Recent ultrastructural research on the course of hair infection and keratin destruction has clearly demonstrated that Piedraia hortae act as keratinolytic fungi, dissolving the cuticular as well as the cortex keratin. In this chapter we will highlight recent findings on these rare hair infections and discuss the keratinophilic and keratinolytic activity of these fungi.