Biofilm formation of Malassezia pachydermatis from dogs.

Yeasts of the genus Malassezia are commensals of the normal skin microbial flora of humans and animals. These yeasts may become pathogenic under certain circumstances and their pathogenic role may be related to host immune system as well to yeast virulence factors (e.g., phospholipase production and biofilm formation). This study aims to evaluate the in vitro ability of M. pachydermatis strains to produce biofilm, and its relationship with phospholipase activity and the genetic make-up of isolates from lesioned (n=32) and healthy (n=30) dog skin. The production of biofilm was determined by crystal violet staining and scanning electronic microscopy (SEM). Biofilm was produced by almost all M. pachydermatis isolates (95.2%) from dogs with and without skin lesions at variable level and different structure. At the SEM, biofilm matrix presented adhering blastoconidia clustered in multi- or monolayer structures with variable quantity of extracellular production. Of the three genotypes detected, genotype B showed the lowest ability to produce biofilm. Of the 59 isolates producing biofilm, 33 (55.9%) produced phospholipase, with a higher biofilm formation (p<0.05) in strains collected from animals with skin lesions. It is here suggested that phospholipase production might act in synergism with the biofilm formation by inducing or exacerbating skin lesions in dogs. The results provide evidences for a better understanding of the interactions between yeasts and host immune system, toward revealing the pathogenicity of M. pachydermatis in animals.