Epidemiology and susceptibility profile to classic antifungals and over-the-counter products of Malassezia clinical isolates from a Portuguese University Hospital: a prospective study.

Purpose: Clinical epidemiological data about the distinct Malassezia species remain scarce. The recurrence of Malassezia-related skin diseases, despite long-term use of antifungals, raises concern about the hypothetical emergence of antifungal resistance. We aimed to assess the distribution of Malassezia species among patients from a University Hospital with pityriasis versicolor, seborrheic dermatitis and healthy volunteers, and to evaluate the susceptibility profile to classic antifungals and over-the-counter compounds, searching for clinical associations.

Methodology: The enrollment of volunteers was conducted at the Dermatology Department of a University Hospital over a 3 year period. Malassezia culture isolates were identified to the species-level by sequencing. The drug susceptibility profile was assessed according to a broth microdilution assay, as recommended by the Clinical Laboratory Standards Institute.

Results: A total of 86 Malassezia isolates were recovered from 182 volunteers. Malassezia sympodialis was the most frequent isolated species. We found high MIC values and a wide MIC range in the case of tested azoles, and very low terbinafine MIC values against most isolates. Previous topical corticosteroid therapy was associated with a significant increase of MIC values of fluconazole and of terbinafine.

Conclusion: Conversely to other European studies, M. sympodialis was the most common isolated species, which might be related to geographic reasons. The impact of previous topical corticotherapy upon the antifungal susceptibility profile was hereby demonstrated. In vitro susceptibility test results suggest that terbinafine might be a valid alternative for Malassezia-related skin diseases nonresponsive to azoles.