Antifungal Resistance Regarding Malassezia pachydermatis: Where Are We Now?

Abstract

Malassezia pachydermatis is a yeast inhabiting the skin and ear canals in healthy dogs. In the presence of various predisposing conditions it can cause otitis and dermatitis, which are treated with multiple antifungal agents, mainly azole derivatives. This manuscript aims to review the available evidence regarding the occurrence of resistance phenomena in this organism. Various findings support the capacity of M. pachydermatis for developing resistance. These include some reports of treatment failure in dogs, the reduced antifungal activity found against yeast isolates sampled from dogs with exposure to antifungal drugs and strains exposed to antifungal agents in vitro, and the description of resistance mechanisms. At the same time, the data reviewed may suggest that the development of resistance is a rare eventuality in canine practice. For example, only three publications describe confirmed cases of treatment failure due to antifungal resistance, and most claims of resistance made by past studies are based on interpretive breakpoints that lack sound support from the clinical perspective. However, it is possible that resistant cases are underreported in literature, perhaps due to the difficulty of obtaining a laboratory confirmation given that a standard procedure for susceptibility testing of M. pachydermatis is still unavailable. These considerations highlight the need for maintaining surveillance for the possible emergence of clinically relevant resistance, hopefully through a shared strategy put in place by the scientific community.

Prevalence and in vitro antifungal susceptibility of commensal yeasts in the external ear canal of cats

“…The highest MIC of ITZ was 4 µg/ml, which was consistent with a previous report of high MIC levels of ITZ (4–8 µg/ml) from planktonic cells of M. pachydermatis isolated from the skin and scales of dogs [ 30 ]. The MICs of KZ at 0.125–0.25 µg/ml observed in 59 % of M. pachydermatis isolates in our study were consistent with previous reports [ 30 , 31 ]. The highest MIC of KZ at 8 µg/ml from this study was consistent with previous findings [ 30 , 31 ].…”

“…The MICs of KZ at 0.125–0.25 µg/ml observed in 59 % of M. pachydermatis isolates in our study were consistent with previous reports [ 30 , 31 ]. The highest MIC of KZ at 8 µg/ml from this study was consistent with previous findings [ 30 , 31 ].…”

“…Most isolates of M. pachydermatis (76 %) showed the same range of MICs for MZ, with many reports at 0.063-16 µg/ml [ 12 , 31 – 35 ]. Interestingly, a high MIC of MZ at ≥ 32 µg/ml was detected in 24 % of our isolates.…”

“…The MICs of ITZ, KZ, MZ, and TERB against M. pachydermatis were evaluated using results modified from a previous report [ 29 – 31 ]. The MIC of ITZ against most isolates of M. pachydermatis in our study was 0.063 µg/ml (78.05 %, 32/41 isolated), which was similar to a previous report of antifungal susceptibility levels of ITZ against M. pachydermatis isolated from otitis and dermatitis dogs and cats [ 29 , 31 ].…”

“…The MICs of ITZ, KZ, MZ, and TERB against M. pachydermatis were evaluated using results modified from a previous report [ 29 – 31 ]. The MIC of ITZ against most isolates of M. pachydermatis in our study was 0.063 µg/ml (78.05 %, 32/41 isolated), which was similar to a previous report of antifungal susceptibility levels of ITZ against M. pachydermatis isolated from otitis and dermatitis dogs and cats [ 29 , 31 ]. The highest MIC of ITZ was 4 µg/ml, which was consistent with a previous report of high MIC levels of ITZ (4–8 µg/ml) from planktonic cells of M. pachydermatis isolated from the skin and scales of dogs [ 30 ].…”