Malassezia species: the need to establish epidemiological cutoff values

Malassezia are common yeasts in human skin microbiome. Under certain conditions these yeasts may cause disease from skin disorders to systemic infections. In the absence of clinical breakpoints, epidemiological cutoff values (ECVs) are useful to differentiate isolates with acquired or mutational resistance. The aim of this work was to propose tentative ECVs of Malassezia furfur, M. sympodialis, M. globosa for fluconazole (FCZ), itraconazole (ITZ), voriconazole (VCZ), ketoconazole (KTZ) and amphotericin B (AMB). A total of 160 isolates (80 M. furfur, 50 M. sympodialis, and 30 M. globosa) were tested. Minimal inhibitory concentrations (MICs) were determined by modified broth microdilution method (CLSI). ECVs were estimated by ECOFFinder software and twofold dilutions beyond the mode. ITZ, KTZ, and VCZ showed the lowest MICs. The highest MIC and widest ranges were for FCZ and AMB. For ITZ, KTZ, and VCZ both ECVs were similar. For FCZ, AMB especially M. furfur, modal ECVs were lower than values obtained by statistical method. When MIC distribution is the only data available, ECV could provide information to help guide therapy decisions. In that drug/species combination in which different peaks in the MIC distribution were observed, difference between both ECV was greater. This is the first study that provides ECV data of 160 Malassezia yeasts. Although ECVs cannot be used as predictors of clinical response, identification of non wild-type isolates suggests that it may be less likely to respond to a given antifungal agent.

Malassezia species causes skin disorders to systemic infections. Epidemiological cutoff value (ECV) allows for differentiation of wild-type and non wild-type isolates. Based on MIC data of 160 isolates we propose tentative ECVs for three Malassezia species. ECVs are useful in surveillance and guide therapy decisions.