This study evaluates how well a vaginal defined medium (VDM) replicates the in vivo metabolic behaviour of key vaginal microbiota members - Lactobacillus crispatus, L. jensenii, and diverse Gardnerella vaginalis isolates - compared to brain heart infusion (BHI) medium.

We used 1H NMR spectroscopy to characterise metabolic profiles during in vitro growth of Lactobacillus and Gardnerella species in VDM and BHI. Differences in metabolite production, growth, acidification, and carbohydrate utilisation were assessed.

Both L. crispatus and L. jensenii grow well in VDM, produce substantially more lactate than in BHI, and acidify the culture more strongly - better reflecting the low pH environment of Lactobacillus-dominant vaginal microbiota. In contrast, G. vaginalis grows less robustly in VDM than in BHI, though key metabolic traits such as the Bifidobacterium shunt and mixed acid fermentation (evidenced by formate production) are preserved. Notably, neither genus consume available glucose, yet still ferment carbohydrates, suggesting a metabolic preference for glycogen over glucose. Evidence of glucose release further indicates glycogen breakdown in culture.

VDM more accurately models the metabolic activity and environmental effects of vaginal Lactobacillus species than BHI, particularly in terms of acidification and lactate production. Although G. vaginalis growth is limited in VDM, its characteristic metabolic pathways remain evident. These findings underscore the value of VDM in modelling key metabolic features of the vaginal microbiota, especially under conditions where Lactobacillus dominate or Gardnerella is prevalent.