The purpose new study published in Frontiers in Microbiology was to elucidate the molecular basis of the interaction among vaginal lactobacilli, the sexually transmitted pathogen C. trachomatis and the epithelial cervical cells. Here, the in vitro activity of 15 Lactobacillus strains belonging to different species—L. crispatus, L. gasseri, and L. vaginalis were evaluated and differentiated from those of C. trachomatis. Specifically, the capability of lactobacilli cells to interfere with C. trachomatis infection in HeLa cells was evaluated. It was observed that Lactobacilli significantly reduced C. trachomatis infectivity and L. crispatus was the most active species. Despite a dose-dependent effect was noticed a significant antagonistic activity was maintained even at lower doses. Whereas, other Gram-positive bacteria—Streptococcus agalactiae, Enterococcus faecalis, and Bacillus subtilis, failed to interfere with C. trachomatis infectivity, thus, Lactobacillus activity proved to be specific.

Additionally, the potential mechanism of protection was investigated in Lactobacillus crispatus BC5, chosen as the model strain. It was found that the incubation of HeLa cell line with BC5 cells induced important modifications in the epithelial plasma membrane, by altering lipid composition and α5 integrin subunit exposure. When α5 integrin subunits were masked by a specific blocking antibody or ITGA5 gene expression was silenced and Chlamydia infection was significantly reduced.

From the results, it was inferred that α5 integrin subunit is crucial for pathogen infection process and the anti-Chlamydia activity can be directly linked to membrane properties modifications in cervical cells. The three Gram-positive bacteria used as controls failed to modify the expression of α5β1 integrin. Hence, a potential molecular mechanism was identified based on the protection exerted by L. crispatus BC5 against C. trachomatis, which provided insights into the role of the cervico-vaginal microbiota for the womans health.