Fluconazole resistance is commonly encountered in Candida auris, and the yeast frequently displays resistance to other standard drugs, which severely limits the number of effective therapeutic agents against this emerging pathogen. In this study, we aimed to investigate the effect of acquired azole resistance on the viability, stress response, and virulence of this species. Fluconazole-, posaconazole-, and voriconazole- resistant strains were generated from two susceptible C. auris clinical isolates (0381, 0387) and compared under various conditions. Several evolved strains became pan-azole-resistant, as well as echinocandin-cross-resistant. While being pan-azole-resistant, the 0381-derived posaconazole-evolved strain colonized brain tissue more efficiently than any other strain, suggesting that fitness cost is not necessarily a consequence of resistance development in C. auris. All 0387-derived evolved strains carried a loss of function mutation (R160S) in BCY1, an inhibitor of the PKA pathway. Sequencing data also revealed that posaconazole treatment can result in ERG3 mutation in C. auris. Despite using the same mechanisms to generate the evolved strains, both genotype and phenotype analysis highlighted that the development of resistance was unique for each strain. Our data suggest that C. auris triazole resistance development is a highly complex process, initiated by several pleiotropic factors.

Candida auris is a globally emerging pathogenic fungus described in Japan in 2009. This fungus has been identified mainly in nosocomial environments, associated with a high frequency of multidrug-resistant strains, and mortality rates reach 60%. C. auris is divided into 6 biogeographic clades, and there is a correlation between the clades and resistance against antifungals. In the current report, 8 strains of C. auris isolated in the Montefiore Medical Center, Bronx were analyzed to assess their clade (via ClaID) and common molecular determinants of antifungal resistance. We assessed antifungal resistance as well as the efficacy of a novel nitric oxide-donating microparticle as an alternative approach against C. auris in vitro through microplate susceptibility tests. Virulence was also determined in a Galleria mellonella model. Our results indicate that 7 out of 8 strains, belonging to clade 1, were resistant to fluconazole, while clade 2 was susceptible. Additionally, the clade 2 strain was more susceptible to treatment with the microparticle, while also being more virulent in an invertebrate model of infection. Our findings were then correlated to visualize parallels between clade identification and resistance/virulence patterns.

Candida auris is an emerging multidrug-resistant pathogen with high transmissibility in healthcare settings. Although echinocandin resistance in Candida is typically associated with fitness loss, we found that micafungin-resistant C. auris strains (MICA^evo) generated from two distinct source isolates (AR0381 and AR0387) via experimental microevolution retained full virulence. Evolved strains developed stable resistance to multiple echinocandins, while AR0387 (B8441), originating from MICA^evo strain, also acquired increased azole tolerance. Whole-genome sequencing revealed clinically relevant mutations in FKS1, as well as changes in genes involved in ergosterol biosynthesis (ERG3), amino acid metabolism, and PKA signaling. Despite in vitro sensitivity to cell wall stressors, resistant strains maintained or even enhanced colonization in a murine systemic infection model. Independently evolved strains showed similar antifungal resistance profiles, and although minor differences of pathogenic potential were noted, no consistent virulence attenuation was observed, indicating the reproducibility of phenotype changes. These findings suggest that C. auris can acquire echinocandin resistance without compromising pathogenicity, supporting its persistence and spread in clinical settings.

The species Candidozyma auris (formerly known as Candida auris) can be subdivided into four major and two minor clades. It is considered an emerging multidrug-resistant pathogen that causes invasive outbreaks around the world. Therefore, the accurate identification of this species plays an important role in combating invasion and facilitating pathogenic management. In our study an optional identification method was developed considering the possibility of using cellular fatty acids (FAs) as a taxonomic and diagnostic tool. FAs were recorded in the collected C. auris strains, and the species characteristic components were determined. Within the isolates examined, the clades were also separated in the statistical analysis. Furthermore, FAs from strains belonging to clade I and II have been divided into two distinct clusters. In testing the performance of the method, all identified samples showed good matches with the established C. auris record in the database without misreading. Taken together, cellular fatty acids were investigated as potential discriminatory biomarkers. The results suggest that this approach can distinguish C. auris from related species and provides distinctive fatty acid profiles for the investigated C. auris clades. The present findings revealed the first report on the application of whole cell FA components as taxonomic features in C. auris.