Metabolism of Lactobacillus and Gardnerella vaginalis in vaginal defined media

Lactobacilli and Gardnerella vaginalis are key bacteria within the vaginal microbiota, significantly impacting its chemical environment. Accurately reproducing vaginal bacteria metabolism in vitro is therefore critical in understanding how this may contribute to vaginal health and disease. Complex media such as brain heart infusion (BHI) support the growth of a wide variety of vaginal bacteria but may not accurately reproduce the conditions found in vivo leading to over- or under-representation of important metabolic processes. Here we use a ¹ H NMR approach to characterise the growth of Lactobacillus crispatus, L. jensenii and a panel of G. vaginalis isolates that differ in their metabolic strategy in a vaginal defined media (VDM). We find that both Lactobacillus species grow well in VDM, produce much more lactate, and consequently acidify the spent culture far more than when cultured in BHI. In contrast, G. vaginalis grows less well in VDM but differences in Bifidobacterium shunt and mixed acid fermentation, previously observed in BHI and evidenced by formate production, are preserved. Importantly neither species consume the available glucose but nevertheless conduct carbohydrate fermentation, implicating a preference for glycogen over glucose metabolism with glucose release evidence of glycogen breakdown. While further work is needed to develop media that can support the growth of a wider variety of vaginal bacteria species and recapitulate all features of their metabolism, VDM nevertheless accurately models the key aspects of the chemical environment when Lactobacillus dominate, and G. vaginalis is prevalent, in the microbiota.