THE HEALTH-PROMOTING EFFECT OF EXTRACELLULAR VESICLES RELEASED BY VAGINAL LACTOBACILLI

Lactobacilli (LB) species dominate the vaginal microflora performing a first line defence against infections (1). Lactobacilli metabolites mediate the health-promoting effect acting as antimicrobials or are used for quorum-sensing and cross-talk communication (2). In this sense, extracellular vesicles (EVs) from LB demonstrate an antimicrobial activity (3,4), modulate host’s nervous and immune system (5) and induce apoptosis in cancerous liver cells (6). Notably, EVs derived from vaginal LB isolates reduce HIV-1 infection (7). Here, we investigate the health-promoting activity of EVs produced by two strains of LB isolated from human vagina (L. gasseri BC12 and L. crispatus BC5) in terms of anti-adhesive effect on pathogens and pro-adhesive effect on LB. EVs were recovered from LB cultures by ultracentrifuge cycles and yield (1010 EVs/mL), size (90-150 nm diameter) and protein content were characterized. Adhesion assays, performed on HeLa cells monolayer, demonstrated that LB-EVs were able to reduce at least 25% the adhesion of all pathogens tested: Escherichia coli, Staphylococcus aureus, Enterococcus faecalis and Streptococcus agalactiae. Moreover, LB-EVs stimulated more than 26% the adhesion of all LB strains, including the same producer strains and two other vaginal isolates belonging to the same species (L. gasseri BC9, BC13 and L. crispatus BC1, BC3). L. gasseri BC12 EVs demonstrated the best health-promoting profile. These results highlighted that the barrier effect exerted by lactobacilli can be mediated by EVs released in the vaginal environment. This opens to the hypothesis of using postbiotics from human vaginal bacteria as a new strategy to prevent/treat human infections.