BACKGROUND: Bacterial vaginosis (BV) is prevalent in ~30% of reproductive-age women globally, increasing risks of sexually transmitted infections and preterm birth. BV promotes genital inflammation, disrupting the epithelial barrier and facilitating pathogen penetration.
We have discovered that lactic acid (LA), a metabolite produced by Lactobacillus-sp, has potent immunobiological activities that may help protect women against BV.
The aim of this study was to investigate the bactericidal activity of LA isomers against vaginal bacteria.
METHODS: Bactericidal activity was determined on cultures ~10⁶ colony forming units (CFU) of L. iners (ATCC55195), L. crispatus (ATCC33820) , and G. vaginalis (ATCC14018) treated with 1%W/V LA isomers (D-LA and L-LA) at pH levels (3.8-7) for 1h under anaerobic conditions. Viability was assessed by quantifying CFU/ml. Bactericidal activity over time was investigated starting with cultures standardised to 0.5 OD and propagated for 24 h with viable bacteria determined as above at different time points. Mixed cultures of G. vaginalis, L. iners, and L. crispatus treated with 1% DL-Lactic acid over 24hs at pH 4.5 were subjected to taxon-specific viability-PCR.
RESULTS: Treatment with LA isomers for 1h showed bactericidal activity against G. vaginalis (50,000-fold reduction, p<0.0001) and L. iners (128-fold reduction, p=0.003), while L. crispatus viability remained unaffected (p>0.93). This activity was more potent than media at the same pH indicating an LA-specific effect. When we analysed the effect of the treatment on mixed cultures for 24h we observed that LA decreased the viability of G. vaginalis and L. iners, but not L. crispatus.
CONCLUSIONS: LA not only targets key BV-associated vaginal bacteria but also the less stable and suboptimal L. iners, which persists following metronidazole treatment of BV. These data reveal a potential antibiotic sparing strategy to promote colonisation with optimal lactobacilli as an option for the treatment for BV recurrence.