Microbiome‐Dependent Modulation of Trichomonas vaginalis Cytotoxicity and Remodeling of the Parasite Secretome

Trichomonas vaginal is a prevalent sexually transmitted parasite whose pathogenicity is shaped by interactions with the vaginal microbiome. While previous studies have shown that host-protective lactobacilli inhibit parasite adhesion and that dysbiotic bacteria enhance pathogenic traits, the extent to which these vaginal bacteria modulate parasite-induced cytotoxicity and its underlying molecular mechanisms remain unclear. Here, we investigated the impact of Lactobacillus gasseri and Gardnerella vaginalis, as representative bacteria of the vaginal microbiome in eubiosis and dysbiosis, respectively, on parasite-induced cytotoxicity and the associated changes in the parasite secretome. Using physiologically relevant epithelial cell models, we show that vaginal L. gasseri strongly inhibits parasite-induced cytotoxicity in a strain- and an exquisite concentration-dependent manner, whereas G. vaginalis enhances cytotoxicity synergistically with the parasite. Proteomic analysis of the T. vaginalis G3 secretome revealed a conserved core set of secreted proteins, including hydrolases and candidate virulence factors, alongside strain-specific variation. Importantly, co-incubation with vaginal bacteria altered the composition and abundance of a few secreted proteins, including proteases and other enzymes implicated in host and bacteria interactions and nutrient acquisition. Together, our findings demonstrate that T. vaginalis cytotoxicity is a context-dependent phenotype shaped by microbial interactions and linked to dynamic remodeling of the parasite secretome. This work highlights the importance of bacterial interactions in modulating parasite pathogenicity and identifies parasite secreted factors as potential candidates that mediate microbiome-dependent pathogenicity.