Origins of vaginal acidity: high D/L lactate ratio is consistent with bacteria being the primary source

BACKGROUND: The origin of the lactic acid that acidifies the vagina is not well established. It is widely accepted that during times of high oestrogen (during the neonatal period and again during a woman's reproductive years) large amounts of glycogen are deposited in the vaginal epithelium and that the glycogen is anaerobically metabolized to lactic acid. What is not esta blished is whether lactic acid is primarily produced by vaginal bacteria or by vaginal epithelial cells. Human cells can make only L-lactate, while ba cteria can produce both D- and L-, thus the D- to L-lactate ratio can indic ate the relative contribution of bacterially derived lactic acid. METHODS: In this study, we used chiral HPLC to examine the percentages of D- and L-l actate in vaginal secretions, in primary cultures of bacteria from these va ginal secretions, and in cultures of lactobacillus isolates of vaginal orig in. RESULTS: We found that in most vaginal secretion samples, >50% of the l actic acid was the D-isoform (mean 55%, range 6-75%, n = 14). CONCLUSIONS: Our results thus support the hypothesis that vaginal bacteria, not epitheli al cells, are the primary source of lactic acid in the vagina.