A urinary tract infection (UTI) is an infection of any part of it. Infections are caused by tiny bacteria-organisms that are only visible under a microscope. The most common cause of UTIs is bacteria. Bacteria that enter the urinary tract are usually quickly removed from the body before they cause symptoms. But sometimes they outgrow the body's natural defenses and cause infection.
Most UTIs are caused by bacteria that live in the intestine. The bacterium Escherichia coli (E. coli) causes most ICUs. The urinary tract has several ways to prevent infections. The sites where the ureters bind to the bladder function as a one-way valve to prevent urine from flowing back into the kidneys, and urination drives the microbes out of the body. In men, the prostate gland produces secretions that slow the growth of bacteria. In both sexes, immune defenses also prevent infections. However, despite these preventive measures, infections occur.