Previous work has shown that the vaginal microbiome decreases in Lactobacillus predominance and becomes more diverse following menopause. It has also been shown that estrogen therapy restores Lactobacillus-dominance in the vagina, and that topical estrogen is associated with OAB symptom improvement. We now know that the bladder contains a unique microbiome, and increased bladder microbiome diversity is associated with OAB. However, there is no understanding of how quickly each pelvic floor microbiome responds to estrogen or if those changes are associated with symptom improvement.
Analysis of data from post-menopausal participants in two trials (NCT02524769 and NCT02835846) who chose vaginal estrogen as their primary OAB treatment and used 0.5 grams of conjugated estrogen (Premarin Cream, (Pfizer, New York City, NY)) twice weekly for 12 weeks. Baseline and 12-week follow-up data included the OAB-q questionnaire and participants provided catheterized urine, vaginal swabs, perineal swabs, and voided urine. Microbes were detected by an enhanced culture protocol. Linear mixed models were used to estimate microbiome changes over time. Urinary AMP activity was assessed by a bacterial growth inhibition assay and correlated with relative abundance of members of the urobiome.
Twelve weeks of estrogen treatment resulted in decreased microbial diversity within the vagina (Shannon, p=0.047; Richness, p=0.043), but not in the other niches. A significant increase in Lactobacillus was detected in the bladder (p=0.037), but not the vagina (p=0.33), perineum (p=0.56), or voided urine (p=0.28). The change in Lactobacillus levels in the bladder was associated with modest changes in urgency incontinence symptoms (p=0.02). The relative abundance of the genus Corynebacterium correlated positively with urinary AMP activity after estrogen treatment.
Estrogen therapy may change the microbiome of different pelvic floor niches. The vagina begins to decrease in diversity and the bladder experiences a significant increase in Lactobacillus levels; the latter is correlated with a modest improvement in the symptom severity sub-scale of the OAB-q.

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