Urine Culture and Sensitivity

The urine culture & sensitivity test is performed to detect and diagnose a microbial infection of the urinary tract. The metabolic processes in the body produce products called metabolites which are present in the blood. Some of them are utilized by cells, while others are wastes which are filtered out of the blood by the kidneys in urine. Urine produced by the kidneys passes through ureters into the urinary bladder where it is stored until the urinary bladder is full. Once full, the urinary bladder releases the urine through another tube called urethra to the outside of the body. The pathway followed by urine from the kidneys to the outside is called the urinary tract. The urinary tract may be infected by some microorganisms causing various conditions. Urine is normally sterile, but if urinary tract infection occurs, the pathogenic microorganism may be found in urine. A urine sample is collected and cultured to detect such an infection and to identify the microorganism causing it.

The collected urine sample is placed on an agar medium (nutrient solution mixed with agarose gel) and incubated at body temperature for 24 to 48 hours. This allows the growth of the microorganisms in the sample if any. Growing microorganisms form different types of colonies on the agar which are studied further in a laboratory to determine the exact microbe causing the UTI.

Once the pathogen is identified, antibiotic susceptibility test is performed to guide treatment for the UTI being tested for. This may be done in two ways. The conventional method involves the use of small filter paper discs with antibiotic of known concentration and placing them on agar plate where the pathogen is cultured. The antibiotic creates a small area around the discs where the microorganisms do not form colonies. The radius of this zone is measured to estimate the efficacy and strength of that antibiotic in treating the UTI. The other method involves an automated machine to detect the sensitivity pattern to find out which antibiotic can be used to treat the infection.