Global transcriptomic response of Malassezia pachydermatis isolates under ketoconazole-induced stress.

Malassezia pachydermatis is an opportunistic yeast associated with otitis externa and dermatitis in dogs. Despite reduced susceptibility to azole antifungals has increasingly been reported in M. pachydermatis, the molecular mechanisms underlying azole stress responses in this species remain poorly understood. In this study, we investigated the global transcriptional response of two M. pachydermatis isolates with different ketoconazole minimum inhibitory concentration values following short-term ketoconazole exposure. Ketoconazole treatment resulted in slightly distinct transcriptional profiles in the two isolates. In isolate 12372, 80 genes were significantly upregulated and 120 were downregulated, whereas isolate 12693 showed 158 upregulated and 211 downregulated genes. Both isolates exhibited significant upregulation of genes involved in ergosterol biosynthesis, including ERG3, ERG5, ERG11, ERG24, and ERG25 suggesting a conserved compensatory response to azole-mediated disruption of sterol metabolism. In isolate 12372, genes associated with ribosome biogenesis was predominantly downregulated, indicating reduced protein synthesis and growth-related activity. In isolate 12693, ketoconazole primarily suppressed genes involved in amino acid biosynthesis, and central carbon metabolism; and upregulated genes associated with ubiquitin ligases, RNA polymerase II regulators, and RNA-binding proteins. Notably, genes encoding ABC transporter-associated efflux pumps were not transcriptionally induced under the tested conditions. Our results provide a comprehensive transcriptomic profile of M. pachydermatis under azole stress, demonstrating that the yeast employs diverse metabolic strategies to enter a decelerated growth state and offer a good basis for identifying future therapeutic targets to combat azole resistance.