Which bacterium is the most common cause of urinary tract infections?

Which bacterium is the most common cause of urinary tract infections? Escherichia coli is the most common cause of urinary tract infections.

E. coli normally lives in the intestines, where it is often harmless or beneficial. Some strains can move from the gut into the urinary tract, usually through the urethra, and multiply in the bladder. This makes E. coli the leading cause of uncomplicated UTIs, especially cystitis.

The bacterium’s success is partly explained by specialized features such as fimbriae, hair-like structures that help it attach to urinary-tract cells. Certain strains can also form protective communities and resist being flushed out by urine. UTIs are more common in women partly because the urethra is shorter and closer to the anus.

Klebsiella pneumoniae, Proteus mirabilis, Enterococcus, and Pseudomonas aeruginosa can also cause UTIs, particularly in hospitals or people with catheters. However, those organisms should not displace E. coli as the standard answer for the most common cause. “UTI” is a broad term covering infections of the urethra, bladder, ureters, or kidneys.