Phenotypic characterization and in vitro antifungal sensitivity of Candida spp. and Malassezia pachydermatis strains from dogs.

Yeasts of the genera Candida and Malassezia can be found as commensal microorganisms in animals. The main species of importance in veterinary medicine are Malassezia pachydermatis and Candida albicans. The objectives of this study were to conduct a phenotypic characterization and to evaluate the in vitro antifungal sensitivity of strains of C. albicans (n=5), C. tropicalis (n=3) and M. pachydermatis (n=32) isolated from dogs. The phenotyping was based on macro and micromorphological features as well as biochemical analysis. The techniques of microdilution in broth and dilution in agar were used to evaluate the in vitro sensitivity of Candida spp. and M. pachydermatis, respectively. The tested drugs were ketoconazole (KTC), itraconazole (ITC), fluconazole (FLC) and amphotericin B (AMB). The morphological analysis of the strains of Candida spp. and M. pachydermatis did not show any noteworthy alterations when compared to standard strains. On the other hand, in the biochemical tests, 34.4% of the strains of M. pachydermatis were negative for the urease test. Four strains of C. albicans were resistant to FLC with a minimum inhibitory concentration (MIC) >64microg/mL and all were resistant to KTC and ITC (MIC>16microg/mL). The MIC for two strains of C. tropicalis were >16microg/mL for KTC and ITC, and >64microg/mL for FLC. It is worth highlighting that all of the strains tested were sensitive to AMB with the MIC varying from 0.25-1.0microg/mL. All strains of M. pachydermatis were sensitive to ITC with a minimum fungistatic concentration (MFC) 0.0075microg/mL. The MIC for 29 strains was the same (MFC0.0075microg/mL) for KTC. The MFCs for FLC varied from 1 to 16microg/mL, and for AMB, the MFC interval was 0.125-8microg/mL. There were no alterations in the classic phenotypic features of the strains of Candida spp. and M. pachydermatis isolated from dogs but, unlike M. pachydermatis, Candida spp. were much more resistant to azole antifungal agents.