White piedra: fungal extracellular matrix formation and its importance in pathogenesis. An ultrastructural study

White piedra is a disease caused by some species of the genus Trichosporon. A case of white piedra was investigated, whose molecular examination identified Cutaneotrichosporon (Trichosporon) debeurmannianum as the causative agent.

Scanning electron microscopy (SEM) was used to examine the affected hairs, as well as the fungal colony of C. debeurmannianum obtained from the hairs. For comparative purposes, a colony of Trichosporon mucoides obtained from a mycotheque was also examined.

Examination of the affected hairs using SEM easily demonstrates nodules on the hair shaft with a predominance of rounded yeast-like structures, adhered to each other by a cementing substance. Examination of the C. debeurmannianum colony demonstrates significant adhesion between the fungal cells by a reticular extracellular matrix. Examination of the T. mucoides colony obtained from a mycotheque demonstrates a small production of fibrillar substance between the blastoconidia.

Examination of the colony obtained from the piedra showed significant formation of extracellular matrix, adhering to and covering the fungal structures, forming a biofilm. This matrix must correspond to the cementing substance described in the condition.

The synthesis of the extracellular matrix must be crucial in the formation of white piedra nodules.