Exploring the role of vaginal lactobacilli derivatives in woman health

The healthy human vaginal ecosystem is most often dominated by either one or a combination of the following Lactobacillus species: Lactobacillus crispatus, Lactobacillus gasseri, Lactobacillus jensenii and Lactobacillus iners. Bacterial derivatives, such as extracellular vesicles (EVs) and exopolysaccharides (EPS), play critical roles in bacteria-host and bacteria-bacteria communication, influencing vaginal ecosystem dynamics. This study investigated vaginal lactobacilli derivatives and their beneficial effects. EVs from L. crispatus BC5 and L. gasseri BC12 were isolated and analyzed for their impact on human epithelium microbial colonization. EPS released by L. crispatus (BC1, BC4, BC5) and L. gasseri (BC9, BC12, BC14) were also studied for their effects on microbial biofilms. Focusing on L. crispatus, a dominant vaginal species linked to health, we explored the role of capsular EPS in biofilm formation and bacteria-host interactions by silencing its biosynthetic pathway. We reported that: i) EVs from L. crispatus BC5 and L. gasseri BC12 enhanced lactobacilli adhesion to human epithelial cells and reduced pathogen adhesion. ii) Released EPS from L. crispatus and L. gasseri enhanced biofilm formation of lactobacilli in a dose-dependent manner while inhibiting pathogen biofilm formation. iii) Genetic manipulation of L. crispatus strains turned out to be challenging, L. crispatus SL9 was the only strain competent for constructing a capsular EPS-deficient mutant. Using this strain as a study model we showed that capsular EPS contribute to the biofilm structure and modify the composition/exposure of some cell-wall molecules, thus affecting lactobacilli adhesion and immunogenicity in the vagina niche. In conclusion, this PhD study gives new insights on the functional role of complex structures and metabolites derived from vaginal lactobacilli concerning women's health and symbiosis. This supports the hypothesis of using EVs and EPS as potential postbiotics with a therapeutic and/or preventive approach to restore/maintain a healthy vaginal ecosystem.