Piedraia hortae: biofilm formation and its importance in the pathogenesis of Piedra nigra (black piedra)

Background Little is known about the ultrastructure of Piedraia hortae. Objective To examine a P. hortae colony with scanning electron microscopy and investigate possible contributions to its pathogenesis. Results On low magnifications, two distinct aspects of the colony are identified, a compact area and a filamentous area. Analysis of the filamentous area demonstrates hyphae adhered by a thin reticular substance. A recurring finding is the adhesion between the fungal filaments in parallel. On high magnifications, the micro fibrillar substance adhering the hyphae to each other becomes very evident. Examination of the compact area shows the hyphae embedded in the reticular matrix forming a biofilm and the colony well adhered. On high magnification, it can be observed that the hyphae are within this fibrillar matrix, which has the same appearance as the filamentous substance that adheres the hyphae to each other. Study limitations Only one strain was examined. Conclusions The formation of biofilm with fungal structures and reticulated extracellular substance is important in the pathogenesis of Piedra nigra.