Ultrastructural Analysis of in Vitro Adherence and Production of Acid Proteases by Clinical Isolates of Candida parapsilosis Sensu Stricto Following Growth in the Presence of Keratinous Substrates from Human Source

Candida parapsilosis is an increasingly important human pathogen. However, little is known about its potential to cause disease. The aims of the present study were to analyse the production of acid proteinases by clinical isolates of C. parapsilosis in the presence of different keratinous substrates from human sources (stratum corneum, nail and hair) and to verify the capability of yeast cells to adhere and grow as biofilm on these substrates. By scanning electron microscopy, it was observed that all C. parapsilosis sensu stricto isolates adhered to the keratinous substrates. For the isolate recovered from onychomycosis, the cell population attached to stratum corneum and hair keratin consisted mainly of blastoconidia. Differently, on nail keratin, pseudohyphae production was observed. Overall, there was a loose association between yeast cells and keratinous substrates. However, on stratum corneum, flocculent extracellular material was seen evolving cells from the onychomycosis isolate by forming a biofilm-like structure. The isolates recovered from onychomycosis and cutaneous lesion produced higher amount of acid proteinases in medium supplemented with nail keratin and stratum corneum keratin, respectively, than that in salt medium (absence of keratin). Furthermore, no differences were observed in the amount of acid proteinases produced by the isolate recovered from tracheal secretion in the media tested (absence and presence of keratin substrates). The information derived from this study will further our understanding of acid proteinase production by C. parapsilosis isolates and provide an insight into pathogenic mechanisms in C. parapsilosis particularly from isolates recovered from superficial mycoses.