Inhibitory effect of Lactobacillus spp. isolated from healthy Korean women on vaginal pathogens

Abstract

Lactobacilli play an important role in vaginal health through production of byproducts such as lactic acid, hydrogen peroxide (H2O2) and bacteroicins. The prevalence of vaginal pathogens as well as the depletion of lactobacilli are both associated with numerous adverse health outcomes including bacterial vaginosis (BV) and vulvovaginal candidiasis (VVC). Among the BV candidate bacterial species, Gardnerella vaginalis, a well-known vaginal pathogen, and Sneathia species are recently emerging as opportunistic pathogens associated with a variety of conditions associated with vaginal infections such as preterm labor, spontaneous abortion, and HPV infection. In this study, we investigated the antimicrobial activities of the supernatant of 51 Lactobacillus strains isolated from 3 healthy subjects on Gardnerella vaginalis, Sneathia sanguinegens (BV pathogens) and Candida albicans (VVC pathogen). Also, we assessed the association between the activities and levels of supernatant pH, D- and L-lactate, and production of hydrogen peroxide. As a results, the tested Lactobacillus isolates were clustered by inhibition patterns against BV and VVC pathogens into four clusters (Cluster Ⅰ~Ⅳ). Lactobacillus isolates belonging to Cluster Ⅳ showed the greatest inhibitory activities to all tested pathogens and significantly higher levels of D-/L-lactate ratio than the other clusters (P <0.0001). To clarify the association between production of lactic acid isomers and pathogen inhibitory effect, we conducted correlation analysis. D-lactate showed significant negative association with the growth rate of all of vaginal pathogens, but no vaginal pathogens associated with L-lactate. Also, to identify the origin specificity of Lactobacillus in terms of lactate isomer producing, we compared the lactate producing patterns of vagina- and gut-originated strains. As a result, we identified that D-lactate was produced by lactobacilli in a species- and origin-specific manner and that D-lactate determines inhibitory patterns of human vaginal lactobacilli isolates on different vaginal pathogens.