Phenotypic and genotypic analysis of <i>Candida albicans</i> vaginal isolates reveals that <i>ECE1</i> expression underpins pathogenicity

ABSTRACT Candida albicans is the leading cause of vulvovaginal candidiasis (VVC), yet the extent to which strain-level variation influences pathogenic mechanisms remains unclear. Candidalysin, a peptide toxin encoded by ECE1 , is a key driver of epithelial damage and immunopathology, but its role has been largely defined in a limited number of laboratory strains. Here, we analyzed a panel of 27 vaginal clinical isolates obtained from asymptomatic, acute VVC, and recurrent VVC (RVVC) subjects and performed whole-genome sequencing and broad phenotypic profiling, including growth, biofilm formation, stressor and antifungal susceptibility, filamentation, and ECE1 expression. To directly assess the role of candidalysin, ece1 Δ/Δ mutant pairs were generated for each isolate and evaluated in vitro and in a murine model of VVC. Isolates exhibited substantial, context-dependent phenotypic heterogeneity, and pathogenic traits did not cluster according to clinical classification. Despite this diversity, deletion of ECE1 universally reduced epithelial damage and inflammatory responses in vitro and attenuated immunopathological markers in vivo . Notably, the reference strain SC5314 displayed enhanced virulence compared to most clinical isolates, further demonstrating that it represents a hypervirulent outlier. Collectively, these findings demonstrate that the virulence determinant candidalysin operates across a highly heterogeneous population of vaginal clinical isolates, and its expression is positively correlated to pathogenicity. These studies further highlight the importance of delineating virulence attributes beyond the lens of SC5314.