Protective Effects of Cell-Free Supernatants from a Kefir-Derived Microbial Consortium against Multidrug-Resistant Candida glabrata Associated with Vulvovaginal Candidiasis

Vulvovaginal candidiasis (VVC) caused by non-albicans Candida species, particularly Candida glabrata, is increasingly associated with treatment failure due to intrinsic or acquired resistance to antifungal drugs. In this study, we explored the anticandidal activity of a postbiotic cell-free supernatant (CFS) obtained from a microbial consortium isolated from homemade kefir (Lactococcus lactis subsp. hordniae, Lactococcus lactis subsp. lactis, and Pichia kudriavzevii) against one reference strain and two multidrug-resistant clinical isolates of C. glabrata. Antifungal susceptibility assays showed a fungistatic effect of CFS (MIC ≥ 500 µg/mL). Pre-treatment with sub-MIC concentrations (100 µg/mL) of CFS significantly reduced C. glabrata planktonic growth, and cell surface hydrophobicity, as well as A-431 vaginal epithelial cell damage. Although total biofilm biomass of C. glabrata was not markedly affected by pre-treatment, metabolic activity was significantly decreased, together with downregulation of key virulence genes (ALS3, ERG11, and FKS1). Subsequently, we explored the effect of the CFS on the inhibition and eradication of biofilms derived from pretreated cells, showing a more marked effect compared to biofilms from untreated cells. Furthermore, in pre-treated fungal cells the CFS almost completely abolished invasive capacity, reducing invasion in epithelial cells model and restored wound healing capacity following infection. Additionally, CFS modulated the host inflammatory response by reducing the expression of pro-inflammatory cytokines in A-431 cells. Overall, the kefir-derived postbiotic attenuated major virulence traits of C. glabrata and promote epithelial protection, providing preliminary evidence supporting its potential as a complementary approach for VVC prevention and management.