Woman holding bladder

Antibiotics may be to blame for recurrent urinary tract infections (UTIs), according to a new study published in the journal Nature Microbiology. UTIs are common infections of the urinary system that typically occur when bacteria enter the bladder through the urethra. While anyone can get a UTI at any time, they are much more prevalent among adult women (via HealthDay News). In fact, research has shown that up to 80% of women will develop a UTI at some point in their lives, and about a quarter of them will develop recurrent infections.

That’s why researchers at the Washington University School of Medicine and the Broad Institute of MIT and Harvard set out to find what was causing these repeat infections. The researchers studied 31 women between the ages of 18 and 45, nearly half of whom experienced recurrent UTIs. They collected and tested their blood and urine samples every month over the course of a year. During this time, a total of 24 UTIs occurred among those with a history of repeated infections, all of whom were treated with antibiotics.

According to the study’s findings, antibiotics provided relief, but only temporarily. That’s because they were able to get rid of disease-causing bacteria in the bladder, but not in the intestines. Researchers found that lingering bacteria in the intestines can multiply and spread to the bladder again, causing another UTI months after the initial infection.

Antibiotics can change the gut microbiome

collection of pills

The study indicated that participants with recurrent UTIs had very different gut microbiomes than participants in the control group. In fact, those who experience repeated infections had much less diversity of healthy gut bacteria, which could make it easier for harmful bacteria to multiply and cause reoccurring infections (via the Washington University School of Medicine). The participants’ gut microbiomes were also less likely to contain bacteria that produce butyrate, a short-chain fatty acid that has anti-inflammatory properties.

According to Dr. Colin Worby, a computational biologist and lead author of the study, the women in the control group were able to eliminate harmful bacteria in their bladders before it resulted in disease. Those who experienced recurrent UTIs were unable to do the same due to the way their gut microbiomes altered their immune response. "Our study clearly demonstrates that antibiotics do not prevent future infections or clear UTI-causing strains from the gut, and they may even make recurrence more likely by keeping the microbiome in a disrupted state," Dr. Worby said in a statement.