How were Lactobacillus species selected as single dominant species in the human vaginal microbiota? Coevolution of humans and Lactobacillus

The optimal microbiota in the vagina for women's health is dominated by single species of Lactobacillus. However, the mechanism by which these species become dominant remains unknown. Therefore, understanding this mechanism is important to establish new treatments, such as probiotics, for vaginal dysbiosis-related conditions. To date, at least 5 hypotheses have been proposed to explain the vaginal dominance of Lactobacillus. However, these hypotheses do not address why a “single” species of Lactobacillus becomes dominant in the vaginal microbiota. First, we evaluated the effect of Lactobacillus culture supernatant on the biomass concentration of each different strain and species of Lactobacillus. The results indicated that the biomass concentrations were not significantly affected by the culture supernatant from other vaginal Lactobacillus species. Then, we discussed host factors that select the vaginal Lactobacillus species and the antagonism of vaginal bacteria. We also assess the mechanism of coevolution of humans and Lactobacillus. Here, we present the hypothesis that host factors such as antimicrobial peptides and proteins (AMPs) and immunoglobulins could play important roles in the selection of specific species of Lactobacillus in the vagina.