What Is the Urinary Microbiome? A Plain-English Guide

The old idea: a sterile bladder

Standard urine tests grow bacteria in a lab dish. If nothing grows, the result is “negative” or “no growth”, and for a long time that was taken to mean healthy urine contained no bacteria at all. The trouble is that many bacteria don’t grow under standard lab conditions.

The discovery

Genetic sequencing changed the picture. Instead of growing bacteria, researchers look for their DNA, specifically a gene called 16S rRNA that is found in all bacteria.

A landmark 2012 study by Alan Wolfe, Linda Brubaker and colleagues, published in the Journal of Clinical Microbiology, collected urine directly from the bladders of women without known infection. To avoid contamination from the skin or vagina, they used a thin catheter through the urethra, and in some women a needle through the lower abdomen into the bladder (suprapubic aspiration). Their key findings:

• Bacterial DNA was found in many samples that were negative on standard culture.
• In 21 of 23 needle-collected samples, bacterial DNA was detected.
• Catheter and needle samples from the same women had very similar bacteria, so catheter collection was reliable for research.

The authors concluded that “uncultivated bacteria are clearly present in the bladders of some women.” They were careful to say that it was not yet clear whether these bacteria were alive.

Since then, many studies have built on this work, and the term urinary microbiome (or “urobiome”) is now widely used.

What lives there?

The bladder’s bacterial community is much smaller than the gut’s and varies from woman to woman. Lactobacillus species, the same family that tends to dominate a healthy vagina, are often found. So are other groups such as Gardnerella and Streptococcus. Researchers are still mapping what a “typical” healthy community looks like, and it may change with age, hormones and menopause.

Why might it matter?

Researchers are exploring whether differences in the urinary microbiome relate to:

• urgency incontinence and overactive bladder;
• recurrent urinary tract infections;
• bladder pain conditions.

Some differences between women with and without symptoms have been reported. But cause and effect is not clear. A different microbiome might contribute to symptoms, result from them, or reflect something else, such as menopause or antibiotic use.

The vaginal connection

The vagina and urethra sit close together, and bacteria can move between them. A vaginal microbiome dominated by lactobacilli, especially L. crispatus, is generally considered protective. This is why researchers tested Lactin-V, an L. crispatus vaginal suppository, in women with recurrent UTIs. In that small trial, 15% of the Lactin-V group had a recurrence compared with 27% on placebo; the overall difference wasn’t statistically significant, but women who stayed well colonized did much better.

What about probiotics and cranberry?

Probiotics: NCCIH reports that a 2015 review of nine studies didn’t find evidence that probiotics prevent UTIs. The NIH Office of Dietary Supplements also points out that probiotic labels often give weight, not the number of live organisms, which makes products hard to compare.

Cranberry: cranberry doesn’t add bacteria; it’s thought to make it harder for some bacteria to stick to the urinary tract. A 2023 Cochrane review found it probably lowers the risk of repeat infections in women with recurrent UTIs.

Where supplement marketing overreaches

The urinary microbiome is a genuine, exciting area of research. That makes it attractive to marketers. Be cautious when you see claims that a product will:

• “repopulate” or “rebalance” your bladder microbiome;
• “eliminate bad bacteria”;
• fix leaks by changing bacteria.

We have not seen evidence that an oral supplement does any of these things in the bladder. Stress incontinence, the most common type of leak in women, is mainly about pelvic floor support, not bacteria.

What you can do now

• Follow evidence-based habits: pelvic floor exercises, bladder training, sensible fluids and less caffeine. See daily habits for bladder control.
• Treat urinary infections promptly and properly with your clinician.
• Avoid unnecessary antibiotics, which can disrupt helpful bacteria (only change prescribed medicines with your doctor).
• If you’re considering a microbiome-themed supplement, read the label for strains and CFU and look for products tested in people. Our FemiCore review shows how we assess one.

Questions researchers are still asking

• What does a healthy urinary microbiome look like at different ages?
• Do the bacteria found in the bladder live there, or arrive from nearby?
• Can changing the microbiome prevent infections or reduce urgency?
• Which interventions, if any, change it reliably?

The bottom line

Your bladder isn’t sterile, and that discovery is changing urology. But the science is young, and products claiming to “balance” your bladder microbiome are ahead of the evidence.

Frequently asked questions

Keep learning

*These statements have not been evaluated by the Food and Drug Administration. FemiCore is not intended to diagnose, treat, cure or prevent any disease. Information on this page is for education only. If you have bladder symptoms such as pain, blood in the urine, fever or sudden changes, see a health care professional.