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.