Isolamento de Microsporum canis, Malassezia spp. e Candida tropicalis em cães: um destaque para teste de sensibilidade de Malassezia pachydermatis in vitro. / Isolation of Microsporum canis, Malassezia spp. and Candida tropicalis in dogs: an emphasis on test sensitivity Malassezia pachydermatis in vitro.

Marilena Ribeiro do Prado

The aim of this study was to investigate the presence of dermatophytes and yeasts in healthy and diseased dogs, as well as to verify the efficacy of the subculture on potato dextrose agar as a complement to the in vitro susceptibility test for Malassezia pachydermatis strains. A total of 633 samples were collected from 26 healthy dogs (104 samples), 131 with dermatitis (343 samples), 74 with otitis (148 samples) and 19 with ocular diseases (38 samples). Fungal identification was based on macro and micromorphologic characteristics, as well as by specific biochemical tests. The microdilution assay was performed in 96-well plates using a modified RPMI 1640 medium. It was observed that 14.3% (2/14) of the positive dermatitis cultures for M. pachyermatis and 40.9% (9/22) of those for Microsporum canis were positive in the direct exam. Direct exam with Gram stais were positive in 84.3% (70/83) if the culture positive samples from otitis. Cultures from healthy animals were positive for M. pachydermatis in 13.5% (7/52) of the samples from the skin, 42.3% (11/26) from the ear and 3.8% (1/26) from the eye. Fungal growth was observed in 20.4% (70/343) samples from animals with dermatitis, with M. canis being the most isolated fungus (n=39), followed by M. pachydermatis (n=30) and Malassezia sp. (n=3). Of the 148 samples from dogs with otitis, 90 (60.8%) were positive for M. pachydermatis and one (0.7%) for Candida tropicalis. Of the clinical specimens from the conjunctiva of animals with ophthalmic disease, only one sample (2.6%) presented positive cultures for M. pachydermatis. Through the antifungic susceptibility analysis, it was observed that the subculture on PDA allows the determination of both MIC and MFC. Therefore, it was observed that all strains (n=50) had shown MIC values of <0.03, 0.03, 2.0 and 4.0 μg/ml and MFC of 0.06, 0.125, 8.0 and 16.0 μg/ml for itraconazole, ketoconazole, voriconazole and fluconazole, respectively. For amphotericin B the MIC/MFC was 4.0 μg/ml. The MIC and MFC for caspofungine was not established and was probably higher than 8.0 μg/ml, which was the highest concentration tested for this drug. We can conclude that, although the importance of direct exam, fungal culture is essential to diminish the quantities of false negative results. The data also evidenced that M. canis was the only dermatophyte and the most isolated fungus from animals presenting dermatitis. In addition, it was verified that the yeast M. pachydermatis is found in healthy animals, as well as in those presenting dermatitis and ocular diseases, and more frequently in dogs with otitis. Finally, the subculture on potato dextrose agar as a complement to broth microdilution assay could be an alternative to the in vitro antifungal susceptibility testing for M. pachydermatis.

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