Kenetta L. Nunn, PhD

   High proportions of Lactobacillus are thought to be important to maintaining vaginal health. Lactobacillus species provide a key function through the production of lactic acid, which is thought to preclude colonization by pathogenic organisms. Four species — L. crispatus, L. iners, L. gasseri, and L. jensenii — typically dominate the communities of most reproductive age women. Communities with low proportions of lactobacilli are often associated with increased susceptibility to sexually transmitted infections (STIs), in addition to other adverse reproductive outcomes. Vaginal community composition differs between women and changes over time. Changes in community composition resulting in low proportions of lactobacilli expose women to windows of risk for STIs. Currently, the mechanisms driving changes in vaginal community composition are poorly understood.

   Figure 1, depicts our current understanding of the factors that possibly determine the abundances of Lactobacillus in the vagina.The abundances of vaginal lactobacilli are often associated with estrogen levels and vaginal glycogen content. Thus, glycogen is thought to support vaginal colonization and proliferation of lactobacilli. However, studies have shown that vaginal lactobacilli cannot directly metabolize glycogen, and that α-amylase likely depolymerizes glycogen to form products that lactobacilli can metabolize. Consistent with this, amylase activity has been demonstrated in vaginal secretions. We expect the differences in community composition are due to variation in the kinds and amounts of resources available to the community, which could be influenced by estrogen and stress.