A urinary tract infection (UTI) typically happens when E. coli from feces heads for the bladder, and yet you can’t just flush the bacteria out when you pee. Researchers have now figured out why that doesn’t work: The pathogen has tiny hooks, and when it feels the pull of urine flow, it holds on tight. The findings are published in Nature Communications this week. 

Many women and some men have suffered from a UTI at some point in their lives. When the intestinal bacterium E. coli travels up the tube that empties urine from the bladder (the urethra), it attaches to the surface of the urinary tract, causing inflammation. It occurs in the bladder most of the time (though infection can spread to the kidneys), and the results are a non-stop urge to pee and a burning pain when you do. 

Previous work revealed that the pathogenic E. coli has long, hair-like protrusions that are tipped with a protein called FimH – which forms a tiny hook. Now, to study the binding behavior of the protein, University of Basel’s Timm Maier and colleagues conducted biophysical and biomechanical tests on isolated FimH molecules. Turns out, when FimH adheres to sugar molecules that coat the surface of cells, it binds more tightly when faced with strong tensile forces – that same “pull” that’s generated during urination.

FimH has two parts: one that binds to the sugar molecules and another, non-sugar binding part that regulates how tightly the first part binds. “When the force of the urine stream pulls apart the two protein domains, the sugar binding site snaps shut,” Maier explains in a statement. “However, when the tensile force subsides, the binding pocket reopens.” When you stop peeing, the bacteria loosen their grip and travel up the urethra toward the bladder. 

Right now, UTIs are generally treated with antibiotics – in fact, they’re the second most common reason antibiotics are prescribed. But resistance to antibiotics is increasing. These new findings might help researchers develop alternative drugs that target FimH attachment specifically in order to prevent the bacteria from hooking on in the first place.