Long-term serial subculture under microaerobic conditions enhances adhesion, reduces antifungal susceptibility, and attenuates virulence in Candida auris

Candida auris is a multidrug-resistant fungal pathogen associated with nosocomial outbreaks worldwide. Although this pathogen may encounter oxygen-limited environments during colonization and infection, the effects of prolonged exposure to reduced oxygen availability on its phenotypic characteristics remain poorly understood. In this study, we serially subcultured C. auris AR 0387 under microaerobic conditions (5% O 2 ) for up to 40 passages, and examined its growth, cellular morphology, adhesion, antifungal susceptibility, virulence, together with sequence analysis of triazole resistance-associated genes and gene expression analysis. Growth characteristics and cellular morphology of strains recovered after microaerobic serial subculture were altered under more severe oxygen limitation (0.1% O 2 ), with no clear growth advantage under these conditions. These strains had enhanced adhesion to polypropylene surfaces, reduced susceptibility to echinocandins and triazole antifungal agents, and attenuated virulence in a Galleria mellonella infection model. These phenotypic characteristics were maintained after subsequent culture under aerobic conditions. No sequence alterations were identified in ERG11 , its 1000-bp upstream region, or TAC1B , whereas changes were observed in the expression of several genes associated with triazole resistance and adhesion, including TAC1B , MRR1 , ALS5 , and SCF1 . These findings suggest that long-term serial subculture under 5% O 2 can be accompanied by persistent changes in multiple phenotypic traits of C. auris , even in the absence of antifungal selection. Further studies are required to determine the molecular mechanisms underlying these changes and their relevance to colonization and infection in vivo .