Urine culture refers to the culture of bacteria in urine and is generally used to diagnose urinary tract infections. Under normal circumstances urine in the human body is sterile, once bacteria invade the organism through the urethra and retrograde into the urinary tract they can cause urinary tract infections. In general, urine specimens containing bacteria are cultured to grow into ring-shaped colonies after 24h or 48h. The size, shape, color and number of these colonies provide clues to identify the type and number of bacteria. If the specimen shows little or no growth after 24h or 48h incubation, the urine culture test can be considered as no bacterial growth and the end of the culture. If more than one type of bacteria is present, further testing is needed to identify the presenting bacteria and to evaluate the ability of the bacteria to grow by drug sensitivity testing to determine which drug therapy is effective in eliminating the infection. Urine specimens for urine culture can be collected at any time of the day, and the external genitalia should be washed before collection due to the presence of bacteria from the epidermis and potential contamination from peri-skin cells during collection. When urinating, some urine is drained and then the mid-phase urine is collected into a container; this method of collection is called mid-phase urine collection or sterile collection.