The urinary system includes the kidneys, bladder and tubes which control water and salt absorption and removal from the blood as waste while also filtering the blood. A urine culture tests for bacteria that may be causing a urinary tract infection, which begins in the urinary system composed of the kidneys, ureters, bladder and urethra. During urinary catheterization, a plastic tube is inserted into the bladder through the urethra to allow urine drainage or treatment injections into the bladder.