L. crispatus protects Hela cells against G. vaginalis cytotoxicity

Abstract

Bacterial vaginosis (BV) is the most common lower genital tract disorder among women of reproductive age and is characterized by a shift in the vaginal flora from the dominant Lactobacillus to a polymicrobial flora, being Gardnerella vaginalis the predominant species of the biofilm mass. However, G. vaginalis vaginal colonization does not always result in BV. Accurate in vitro model systems mimicking in vivo conditions are required to better understand the complex host-microbe and microbe-microbe interactions. In effort to analyse the adaptation and interaction of the commensal vaginal microbiota and pathogens in the vaginal environment, we used a genital tract simulant medium (mGTS) to evaluate the growth of resident vaginal Lactobacillus crispatus and G. vaginalis in the adopted growth medium. Also, to understand the differences between G. vaginalis strains isolated from women with and without BV, we performed in vitro assays to compare the virulence properties of G. vaginalis strains. In this sense, G. vaginalis strains were characterised for their cytotoxicity activity after adhesion on a monolayer of epithelial cells pre-adhered with L. crispatus, mimicking the healthy vagina environment. Furthermore, transcript levels of vaginolysin and sialidase genes were also evaluated. These assays revealed that a BV isolate of G. vaginalis was significantly more cytotoxic than a non-BV isolate after 3 hours in the contact with a monolayer of HeLa cells. However, when L. crispatus was pre-adhered on a monolayer of HeLa cells, the cytotoxicity effect of both strains observed was drastically reduced. Significant differences in the transcript levels of both genes were also observed in the presence of L. crispatus. Thus, this work highlights not only the discrepant virulence potential of two distinct variants of G. vaginalis but also the beneficial role of vaginal lactobacilli in protecting the vaginal epithelium from G. vaginalis infection.