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

Abstract

Background: 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.

Methods: 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.

Results: 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.

Discussion: 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.

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

Keywords: Extracellular matrix; Scanning electron microscopy; White piedra.

Figure 1

(A) Colony with creamy aspect. (B) Optical microscopy – predominance of blastoconidia with some hyphae.

Figure 2

SEM of white piedra ‒ (A) Low magnification identifying nodules in the hair (×130). (B) Detail of the nodule, with initial lesion on the left (×1,100). (C) High magnification demonstrating clusters of blastoconidia (×2,200). (D) High magnification with blastoconidium on the surface (×10,000).

Figure 3

SEM of the C. debeurmannianum colony with a predominance of blastoconidia and some hyphae (×1.400).

Figure 4

SEM of the C. debeurmannianum colony – detail of the blastoconidia adhered by reticular extracellular matrix, forming clusters resembling acini (×5.500).

Figure 5

SEM of C. debeurmannianum colony ‒ (A) High magnification of blastoconidia covered by extracellular matrix (×6,000). (B) Detail of covered blastoconidia and adhered to each other (×8.500).

Figure 6

SEM of C. debeurmannianum colony – detail of dense extracellular matrix covering the blastoconidia (×13.000).

Figure 7

SEM of the C. debeurmannianum colony – detail of the extracellular matrix formation also by hyphae (×7.000).

Figure 8

SEM – comparative demonstration of the similarity between the appearance of the white piedra nodule (A; ×2,500) and the C. debeurmannianum colony (B; ×2.200).

Figure 9

SEM of T. mucoides colony – (A) Fungal filaments and blastoconidia not adhered by extracellular matrix (×1,500). (B) Detail of blastoconidia with discrete extracellular matrix production (×7.000).