Clinical meaning
The healthy vaginal microbiome is dominated by Lactobacillus species (L. crispatus, L. iners, L. jensenii, L. gasseri), which maintain an acidic pH (3.8-4.5) through lactic acid production from glycogen metabolism. Lactobacilli produce both D- and L-lactic acid isomers, hydrogen peroxide, and bacteriocins that collectively inhibit pathogenic bacterial colonization. L. crispatus is considered the most protective species, producing the highest levels of D-lactic acid (a more potent antimicrobial isomer) and maintaining the most stable community state type (CST-I). Bacterial vaginosis (BV) represents a dysbiotic shift from Lactobacillus-dominant to a polymicrobial community dominated by Gardnerella vaginalis, Atopobium vaginae, Prevotella bivia, Mobiluncus species, and Megasphaera. G. vaginalis initiates BV by forming a biofilm on the vaginal epithelium - a structured polymicrobial community encased in an extracellular polysaccharide matrix that confers antibiotic resistance. This biofilm persists after standard metronidazole therapy in up to 50% of cases, explaining the high recurrence rate (50-80% within 12 months). BV biofilm produces sialidases and prolidases that degrade cervical mucus and vaginal epithelial protective factors, and amines (trimethylamine, putrescine, cadaverine) that produce the characteristic fishy odor and elevate vaginal...