A urine culture is a test to find and identify germs (usually bacteria) that may be causing a urinary tract infection (UTI) . Urine in the bladder normally is sterile-it does not contain any bacteria or other organisms (such as fungi).But bacteria can enter the urethra and cause an infection.A urine sample is kept under conditions that allow bacteria and other organisms to grow. If few or no organisms grow, the test is negative. If organisms grow in numbers large enough to indicate an infection, the culture is positive. urine sample is kept under conditions that allow bacteria and other organisms to grow. If few or no organisms grow, the test is negative. If organisms grow in numbers large enough to indicate an infection, the culture is positive.