Oral probiotics and the female urinary microbiome: a double-blinded randomized placebo-controlled trial

Purpose Probiotics may reduce risk of urinary tract infection by preventing colonization of uropathogens. We aimed to determine the change in the ratio between uropathogens:Lactobacillus (U/L) within the lower urinary tract in response to oral probiotic. Methods This was a double-blinded randomized controlled trial of healthy pre-menopausal female volunteers. Participants provided daily voided urine for 3 months including three phases of the trial: 1-baseline, 2-intervention, 3-wash-out. Participants were randomized to an oral probiotic (Lactobacillus rhamnosus GR-1 and Lactobacillus reuteri RC-14) versus placebo. The primary outcome was the U/L ratio of daily voided urine, as determined by an enhanced urine culture method. Analysis included t test of the ratios and separate generalized linear mixed effects models (GLMM) for microbiota diversity. Results 481 samples of seven female participants with mean age 29.1 years (+/- 5.3 years) were included in the analysis (probiotic n = 4; placebo n = 3). No adverse events were reported. The placebo and probiotic groups had similar mean U/L ratios with no difference between placebo and probiotic groups in Phases 1-3 (p = 0.90, p = 0.58 and p = 0.72, respectively). The probiotic species were never identified in the voided urine. There were no changes between groups in terms of microbiota diversity. Conclusion For young healthy women, the use of oral probiotic did not affect the U/L ratio.