Anti-bacterial activity of 17 strains of lactobacilli against elementary bodies of Chlamydia trachomatis

Chlamydia trachomatis (CT) is the most frequent bacterial sexually transmitted infection (STI) worldwide. The human vaginal microbiome plays a crucial role in preventing a large number of urogenital diseases, including STIs. These protective functions are mainly attributed to Lactobacillus species dominating the vaginal niche of healthy women. Up to now, fes studies have investigated the possible interaction between lactobacilli and CT. The aim of our study was to investigate the anti-bacterial activity of 17 vaginal lactobacilli isolates against elementary bodies (EBs) of CT in relation to their metabolic profile. Seventeen Lactobacillus strains, isolated from vaginal swabs of healthy pre-menopausal women were used. Lactobacilli cultures were centrifuged to separate cell pellets (CP) from cell-free supernatants (CFS). All CP and CFS corresponding to 2.5×108, 2.5×107 and 2.5×105 CFU were mixed with 5×103 IFU of EBs of CT, serotype D. Tubes were incubated for 7, 15 and 60 minutes and then centrifuged. Supernatants were used to infect confluent Hela cells. CT infectivity was evaluated after 48h of incubation. 1H-NMR analysis of metabolic profiles of CFS was conducted on AVANCE spectrometer. Statistical analysis were performed using GraphPad Prism Software, applying Wilcoxon test. CT infectivity was significantly reduced only by CFS (p=0.038), in contrast to CP (p=0.425). CSF at the highest concentration showed the strongest anti-chlamydial activity. Under these conditions CFS were found to have pH<4.5, differently from the less concentrated ones. The best anti-Chlamydia profile was shown by L. crispatus species. Production of lactate and acidification of the vaginal environment seemed to be crucial for the activity, in addition to the consumption of the carbonate source represented by glucose. Our results demonstrate the ability of different Lactobacillus strains of vaginal origin to inactivate C. trachomatis EBs through the production of extracellular metabolites. The final goal is the selection of active lactobacilli in order to develop new pharmaceutical formulations based on probiotics for the prevention and treatment of CT infection