İnvestigation of the resistance of trichosporon asahii strains to azole group antifungals using phenotypic and molecular methods

Over the past 30 years, cases of Trichosporon asahii have increasingly been isolated globally, particularly in immunocompromised individuals. Recently, there has been an observed rise in resistance to azole antifungals, which are considered the most effective treatment option. Despite this increase in resistance, the mechanisms behind it are not yet fully understood. Between 2014 and 2024, 20 T. asahii isolates, identified using MALDI-TOF MS, were included in this study from clinical samples received at Istanbul University-Cerrahpaşa, Cerrahpaşa Medical Faculty Hospital. The aim was to determine the antifungal resistance profiles of these isolates and to investigate the molecular mechanisms behind resistance to azole antifungals. To determine the antifungal susceptibility profiles, Thermo Scientific Sensititre YeastOne susceptibility microplates were used. The susceptibility to the following antifungal agents was evaluated: fluconazole (FZ), voriconazole (VOR), itraconazole (IZ), posaconazole (PZ), amphotericin B (AB), 5-flucytosine (FC), anidulafungin (AND), caspofungin (CAS), and micafungin (MF). The antifungal susceptibility results were as follows: FZ: MIC 50 >4, MIC 90 >4; VOR: MIC 50 >0.12, MIC 90 >0.12; IZ: MIC 50 >0.25, MIC 90 >0.5; PZ: MIC 50 >0.5, MIC 90 >0.5; AB: MIC 50 >2, MIC 90 >4; FC: MIC 50 >16, MIC 90 >32. As anticipated, the echinocandin class antifungals CAS, AND, and MF showed resistance with MIC values >8 mg/ml. The ERG11 gene from the 20 isolates was sequenced using the Sanger sequencing method. Four distinct variants were identified: a 14-bp insertion in three isolates, an 8-bp insertion in three other isolates, and a 13-base change occurring after position 282 in two isolates. A correlation between these mutations and the antifungal susceptibility profiles was observed, with similarities noted among the isolates exhibiting these changes.