Urine itself functions as an antiseptic, washing potentially harmful bacteria out of the body. The ureters are designed to prevent urine from backing up into the kidney. The prostate gland in men secretes infection-fighting substances. The immune systems itself in both sexes continuously fight bacteria and other harmful micro-invaders. In addition, the immune system defenses and antibacterial substances in the mucus lining of the bladder eliminate many organisms.
Acid is hostile to other bacteria.
Lactobacilli also produce hydrogen peroxide, which helps eliminate bacteria and reduces the ability of E. coli to adhere to vaginal cells. In so doing, they shed away from the lining, carrying the bacteria with them. Much less often, bacteria spread to the kidney from the bloodstream. Bacteria in the urinary tract also accounts for other conditions, including asymptomatic bacteriuria and acute urethral syndrome . Cystitis is the most common urinary tract infection.