Ultrastructural aspect of the keratinolytic activity of piedra
María José Figueras and Josep Guarro
Departament de Microbiologia, Facultat de Medicina, Universitat Rovira
i Virgili, Reus, España
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
In: Kushwaha RKS, Guarro J (Eds.). Biology
of Dermatophytes and other Keratinophilic Fungi.
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Revista Iberoamericana de Micología, Bilbao, 2000.