Bacterial vaginosis is associated with increased amylolytic activity

Glycogen is the most abundant vaginal carbohydrate in reproductive aged women. Reduced vaginal glycogen is associated with lower levels of Lactobacillus crispatus, overgrowth of fastidious anaerobes such as Gardnerella vaginalis and increased risk of adverse reproductive and sexual health outcomes. Here we show that Gardnerella vaginalis, Lactobacillus iners and Lactobacillus crispatus can autonomously utilize glycogen as a source for growth. Using an ungelatinized and labeled form of raw amylose, a more degradation-resistant α-1,4-glucan, we were able to discriminate between the alpha-glucosidase activities of common vaginal bacterial species. The bacteria Lactobacillus crispatus, Lactobacillus iners, Gardnerella piotii as well as several other common vaginal species were not capable of raw amylose degradation, while Gardnerella vaginalis, Gardnerella swidsinskii and Gardnerella leopoldii were, with the latter two having the highest degradation rates. In contrast to the glycogen-degrading activity we previously identified in Lactobacillus crispatus, this Gardnerella alpha-glucosidase activity was not cell-bound and not repressed in the presence of glucose. Raw amylose degradation activity in vaginal swabs was strongly associated with bacterial vaginosis as assessed by Nugent scoring. Overall, our results show that the dysbiotic microbiota of bacterial vaginosis is associated with increased amylolytic activity, which is also found in pure cultures of Gardnerella species, but not in other common vaginal bacteria.