Prevalence and genetic diversity of azole-resistant Malassezia pachydermatis isolates from canine otitis and dermatitis: a two year study

Abstract

Despite previous reports on the emergence of Malassezia pach y dermatis strains with decreased susceptibility to azoles, there is limited information on the actual pre v alence and genetic diversity of azole-resistant isolates of this yeast species. We assessed the prevalence of azole resistance in M. pach y dermatis isolates from cases of dog otitis or skin disease attended in a veterinary teaching hospital during a 2-year period and analyzed the ERG11 (encoding a lanosterol 14- α demethylase, the primary target of azoles) and whole genome sequence diversity of a group of isolates that displa y ed reduced azole susceptibility. Susceptibility testing of 89 M. pach y dermatis isolates from 54 clinical episodes (1-6 isolates/episode) re v ealed lo w minimum inhibitory concentrations (MICs) to most azoles and other antifungals, but 11 isolates from six different episodes (i.e., 12.4% of isolates and 11.1% of episodes) had decreased susceptibility to multiple azoles (fluconazole, itraconazole, ketoconazole, posaconazole, ravuconazole, and/or voriconazole). ER G11 sequencing of these 11 azole-resistant isolates identified eight DNA sequence profiles, most of which contained amino acid substitutions also found in some azole-susceptible isolates. Analysis of whole genome sequencing (WGS) results re v ealed that the az ole-resistant isolates from the same episode of otitis, or e v en dif ferent episodes af fecting the same animal, were more genetically related to each other than to isolates from other dogs. In conclusion, our results confirmed the remarkable ERG11 sequence variability in M. pachydermatis isolates of animal origin observed in previous studies and demonstrated the value of WGS for disentangling the epidemiology of this yeast species.