D-lactic acid inhibits Candida albicans associated with vulvovaginal candidiasis: in vitro and in vivo effects and underlying mechanisms

Candida albicans is a major opportunistic fungal pathogen responsible for invasive and superficial infections such as recurrent vulvovaginal candidiasis, and increasing drug resistance underscores the need for new antifungal agents. D-lactic acid (D-LA), a metabolite produced by Lactobacillus spp., has been proposed as a candidate, yet its activity and mechanisms against C. albicans remain unclear. In this study, we evaluated the antifungal effects of D-LA on C. albicans SC5314, examining growth, hyphal morphogenesis, and biofilm formation through broth microdilution, hyphal induction/inhibition assays, crystal violet staining, and XTT metabolic analysis. Membrane integrity was assessed by trypan blue exclusion and live/dead staining, and transcriptomic changes were profiled by RNA-seq and validated by qRT-PCR. We further tested efficacy in a mouse model of vaginal candidiasis. D-LA markedly inhibited hyphal formation and biofilm development, reduced biofilm biomass and metabolism, and induced membrane damage. Transcriptomic and qRT-PCR analyses showed downregulation of virulence-associated genes (ECE1, TEC1, ALS1) and upregulation of the pH-responsive gene PHR2. D-LA showed minimal cytotoxicity toward VK2/E6E7 epithelial cells, and in vivo experiments demonstrated potent antifungal efficacy with a favorable safety profile.