Susceptibility Testing of Environmental and Clinical Aspergillus sydowii Demonstrates Potent Activity of Various Antifungals

The genus Aspergillus consists of a vast number of medically and environmentally relevant species. Aspergillus species classified in series Versicolores are ubiquitous in the environment and include the opportunistic pathogen Aspergillus sydowii, which is associated with onychomycosis and superficial skin infections. Despite frequent clinical reports of A. sydowii and related series Versicolores species, antifungal susceptibility data are scarce, hampering optimal treatment choices and subsequent patient outcomes. Here, we employed antifungal susceptibility testing (AFST) based on microbroth dilution on a set of 155 series Versicolores strains using the common antifungals amphotericin B, itraconazole, voriconazole, posaconazole, isavuconazole and micafungin with the addition of luliconazole and olorofim. All strains were identified using partial calmodulin gene sequencing, with 145 being A. sydowii, seven A. creber and three A. versicolor, using the latest taxonomic insights. Overall, tested antifungals were potent against the entire strain collection. In comparison to A. fumigatus, azole and amphotericin B MICs were slightly elevated for some strains. AFST with luliconazole and olorofim, here reported for the first time, displayed the highest in vitro activity, making these antifungals interesting alternative drugs but clinical studies are warranted for future therapeutic use.