Vaginal pH measured in vivo: lactobacilli determine pH and lactic acid concentration.

BACKGROUND: Lactic acid (protonated lactate) has broad antimicrobial activity. Vaginal lactobacilli produce lactic acid, and are known to confer protection against reproductive tract infections when they are predominant in the vaginal microbiota. Using novel ex vivo methods, we showed that cervicovaginal fluid (CVF) from women with a predominantly lactobacilli-morphotype microbiota contains significantly more lactic acid than previously thought, sufficient to inactivate reproductive tract pathogens. Here, we measured vaginal pH in vivo in 20 women with a predominantly lactobacilli-morphotype (low Nugent score) microbiota. We also investigated the in vitro production of protons (as hydrogen ions) and lactate by vaginal lactobacilli. RESULTS: The average vaginal pH in these women was 3.80 ± 0.20, and the average lactate concentration was 0.79% ± 0.22% w/v, with pH and lactate concentration tightly correlated for each sample. In vitro, lactobacilli cultured from these CVF samples reached an average pH of 3.92 ± 0.22, but the average lactate concentration was only 0.14% ± 0.06% w/v, approximately five-fold less than in the corresponding CVF samples. When the pH of the cultures was raised, lactate and hydrogen ion production resumed, indicating that production of lactate and hydrogen ions by vaginal lactobacilli is limited primarily by their sensitivity to hydrogen ion concentration (low pH) not lactate concentration. CONCLUSIONS: Some vaginal lactobacilli cultures have a lower limiting pH than others, and limiting pHs in vitro showed good correlation with pHs measured in vivo. The limiting pH of the lactobacilli predominant in a woman's vaginal microbiota seems critical in determining the concentration of antimicrobial lactic acid protecting her.

The Impact of Vaginal Probiotics on Pessary Use: A Randomized Controlled Trial.

IMPORTANCE: Pessary-related adverse effects are common, and treatment options are limited. Probiotics may improve pessary-related adverse effects by altering the vaginal microenvironment. OBJECTIVE: This study aimed to evaluate the effect of a vaginal probiotic suppository on the vaginal microenvironment among pessary users. STUDY DESIGN: Women who used pessaries were randomized to vaginal probiotic suppository use versus without use. The intervention was a vaginal probiotic suppository and moisturizing vaginal gel. The vaginal microenvironment was assessed using Gram stain and Nugent's criteria at baseline and 3 months by a microbiologist blinded to group allocation. Symptoms and experience with use of the probiotic were assessed using questionnaires. The primary outcome was change in lactobacilli count on Nugent subscore at 3 months. RESULTS: A total of 147 postmenopausal women were randomized (86 to the intervention arm and 61 to the control arm), and 124 (87.9%) presented for a 3-month follow-up. There was no difference between the arms in age, race, body mass index, and Charlson Comorbidity Index. A majority of participants had the pessary managed by the health care professional (intervention arm vs control arm, 46 [76.7%] vs 55 [68.8%]; P = 0.30). Composition of the vaginal microenvironment did not differ with or without probiotic treatment at 3 months. Bother from vaginal symptoms, including discharge, itching, and discomfort, did not differ between arms. Adverse effects from the intervention were minor, resolved with discontinuation, and occurred at 39.1%. CONCLUSION: Vaginal probiotic suppository use did not affect the composition of the vaginal microenvironment, patient satisfaction, or vaginal symptoms after 3 months of use in pessary users.