Overactive Bladder

The Bacteria Living in a Bladder That Was Thought Empty

Researchers are still early in working this out, and the studies are small and not always consistent. Overactive bladder means urgency, needing to pass urine often, and sometimes leaking before reaching a toilet. It affects more than 16.5% of adults and its cause has never been well explained. One assumption underpinning that gap has recently turned out to be wrong.

Urine was never sterile

For most of the twentieth century, a negative urine culture was taken to mean no bacteria present.

That conclusion came from the method. Standard culture is designed to grow the handful of species that cause obvious infections, using conditions and timings suited to them. Anything slow-growing or oxygen-averse simply doesn't appear.

When researchers used expanded culture techniques and genetic sequencing instead, they found resident bacterial communities in the bladders of healthy people.

That changed the question. Instead of asking whether bacteria are present in a bladder without infection, researchers could ask whether the community differs when symptoms are there.

What the comparisons found

Several groups have now compared bladder bacteria in women with urgency and leakage against women without symptoms.

Using catheter-collected urine, so the sample doesn't pick up bacteria from elsewhere, researchers found Gardnerella increased and Lactobacillus decreased in the symptomatic group. Nine bacterial genera were cultured more often from them.

The Lactobacillus finding split by species, which matters because they're often treated as one group. Lactobacillus gasseri was more common in women with urgency and leakage. Lactobacillus crispatus was more common in the women without symptoms.

A later study looking at bladder muscle activity found the same pattern for those two species.

So the difference isn't simply more bacteria or fewer. It's which ones.

Source: Differences in the Urinary Microbiome of Patients with Overactive Bladder Syndrome with and without Detrusor Overactivity on Urodynamic Measurements

A finding with practical consequences

One result stands out for being about treatment rather than description.

Researchers examined whether the bacterial community in the bladder related to how well women responded to standard medication for urgency and leakage.

It did. The composition present beforehand was associated with how much benefit people got.

That's an early finding in a small group, and it hasn't yet changed practice. It does suggest a possible explanation for something clinicians see constantly, which is that these medications help some people substantially and others barely at all.

Source: The Current Evidence on the Association Between the Urinary Microbiome and Urinary Incontinence in Women

Where the gut comes in

The bladder community doesn't arrive from nowhere, which is where the intestine enters.

Bacteria reach the bladder from the gut and the surrounding skin, so the gut is the upstream source for much of what ends up there.

A study comparing people with urgency symptoms against people without them found their gut bacteria differed too, though this has been examined far less than the bladder side.

There's also a straightforward mechanical link. Constipation is strongly associated with urgency and frequency, because a loaded bowel presses directly on the bladder and reduces the volume it can hold comfortably. Gut bacteria substantially influence how easily and regularly the bowel empties.

That second route is the least glamorous and the best established.

What this means for you

Sudden urgency, frequent trips to the toilet or leaking before reaching one is worth taking to a doctor, since bladder training, pelvic floor exercises and medication all help and infection needs ruling out first. In addition, the research above found the bladder holds its own bacterial community that differs when symptoms are present, and constipation independently worsens urgency by reducing how much the bladder can hold. A varied, plant-rich diet supports the same gut bacteria this research ties to regular bowel movements and a steadier community upstream of the bladder. That's the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.