Abstract
The genus Malassezia includes lipophilic yeasts, which are part of the skin microbiota of various mammals and birds. Unlike the rest of Malassezia species, M. pachydermatis is described as non-lipid-dependent, as it is able to grow on Sabouraud glucose agar (SGA) without lipid supplementation. In this study we have examined the phenotypic variability within M. pachydermatis and confirmed its lipid-dependent nature using a synthetic agar medium. We used a selection of representative non-lipid-dependent strains from different animal species and three atypical lipid-dependent strains of this species, which were not able to grow after multiple passages on SGA. More than 400 lipid-dependent Malassezia isolates from animals were studied in order to detect the three lipid-dependent strains of M. pachydermatis. The identity of the atypical strains was confirmed by DNA sequencing. On the other hand, we have modified the Tween diffusion test, which is widely used in the characterization of these yeasts, by using a synthetic agar-based medium instead of SGA. This modification has proved to be useful for differentiation of M. pachydermatis strains, providing reproducible results and a straightforward interpretation. The finding of these peculiar lipid-dependent strains exemplifies the large variability within the species M. pachydermatis, which involves rare atypical strains with particular growth requirements.
Highlights
The genus Malassezia includes lipophilic yeasts, which are part of the skin microbiota of various mammals and birds
Unlike the rest of Malassezia species, M. pachydermatis is described as non-lipid dependent, as it is able to grow on Sabouraud glucose agar (SGA) without lipid supplementation
The isolation of M. pachydermatis strains unable to grow on SGA has been rarely reported [7,8,9]
Summary
The genus Malassezia includes lipophilic yeasts, which are part of the skin microbiota of various mammals and birds. The genus includes 17 species [1, 2], three of which have been recently proposed [3, 4] Of all these species, M. pachydermatis is a zoophilic yeast frequently isolated from the skin of wild and domestic carnivores. M. pachydermatis is part of the normal microbiota of the skin and ear canal of these animals, under some predisposing factors it can overgrow and lead to the development of dermatitis and otitis. These diseases are common in dogs, and occur less frequently in other animals [5].
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