Differential Biofilm Susceptibility and Potent Isavuconazole Post-Antifungal Effect Distinguish Cutaneotrichosporon dermatis from Trichosporon asahii

The study examined the differences between Cutaneotrichosporon dermatis and Trichosporon asahii, two yeast-like fungi that can cause infections in humans. The researchers performed various tests, including morphological and molecular identification, pathogenicity assessment, biofilm formation and eradication assays, antifungal susceptibility testing, drug combination effects, and post-antifungal effect (PAFE) comparisons.

Cutaneotrichosporon dermatis was identified as such through ITS/IGS1 sequencing and phylogenetic analysis. The fungus grew better at 37°C compared to 25°C. In tests with insects, C. dermatis, Trichosporon asahii, and Candida albicans all displayed varying levels of pathogenicity, with Rhizopus oryzae being the most potent per cell.

Biofilms formed by C. dermatis were more effectively inhibited by terbinafine (TRB) and amphotericin B (AmB) than by azole agents, which only showed partial inhibition even at high concentrations. Susceptibility testing indicated a relatively strong response to AmB and azole agents.

When tested alongside either TRB or azole agents, the combination showed synergy, as the fractional inhibitory concentration index (FICI) was below 0.5. Perhaps most notably, isavuconazole (ISC) demonstrated a significantly stronger PAFE than the other tested azoles. Despite azoles showing only partial efficacy against C. dermatis biofilms, the fungus can still lead to invasive infections.

These findings suggest that azole monotherapy, TRB and azole combination therapy, and the potent PAFE of ISC could be effective treatment options for C. dermatis infections.