Urine Culture Procedure

A urine culture is a test that can detect bacteria in your urine. This test can find and identify the germs that cause a urinary tract infection (UTI). Bacteria, which typically cause UTIs, can enter the urinary tract through the urethra. In the environment of your urinary tract, these bacteria can grow rapidly and develop into an infection.

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Sample Required

Urine culture is used to diagnose bacterial urinary tract infection of the urinary bladder, kidneys, ureter, and urethra.

1. Pyuria is the pus in the urine and bacteriuria, both indicate urinary tract infections.
2. The early morning sample is the best sample because it has a maximum number of bacteria.
3. Collect 3 to 5 mL of urine in the sterile container.
   1. Other methods are catheterization or aspiration of a suprapubic or indwelling catheters.
4. Urine from the collection urine bag is not a good sample.
5. Try to collect the urine sample before starting the antibiotics.
6. A bacterial count of >100,000 colonies/mL indicates infection.
   1. A bacterial count <10,000 colonies /mL indicates contamination and less chances for infection..

Procedure:

• Tip over the container to re-mix the urine sample.
• Remove the cap and dip the end of a sterile 1-µL inoculating loop (white) into the urine and remove it vertically making sure that there is no urine up the loop.
• Tip and spread the inoculum over the surface of a standard nutrient agar plate (60 × 15 mm) prepared according to the instructions of the manufacturing company.
• Re-dip the end of the same 1-µL loop into the urine and remove it vertically making sure that there is no urine up the loop.
• Tip and spread the inoculum over the surface of a glucose-topped MacConkey agar plate (60 × 15 mm). Spread as described above. Prepare the glucose-topped MacConkey agar plates as following:
  • Disinfect the port of a bag of 5% glucose intravenous infusion solution (1000 mL) with 70% isopropyl-alcohol-impregnated cotton ball or pad and allow to dry.
  • Aspirate 2 mL of the 5% glucose solution using a sterile needle and syringe.
  • Drop the aspirated solution on the surface of a standard MacConkey agar plate (60 × 15 mm) prepared according to the instructions of the manufacturing company.
  • Spread it by tilting the plate in different directions.
  • Leave the plate on the bench at room temperature for at least 1 h in order to allow the solution to infuse and the surface to dry.
• Re-dip the end of the same 1-µL loop into the urine and remove it vertically making sure that there is no urine up the loop.
• Tip and spread the inoculum over the surface of a standard MacConkey agar plate (60 × 15 mm) prepared according to the instructions of the manufacturing company. Spread as described above.
• Incubate the plates aerobically at 35–37 ◦C for at 18–24 h.
• In the following day, count the number of colonies on the surface of each medium. Each colony growing on the agar plate represents one colony forming unit (cfu)/µL (according to the size of the loop), which is equal to 1000 cfu/mL. Remember that nutrient agar is the primary medium used for counting colonies.

Common Bacteria:

Interpretation:

Common Antibiotic Discs Use in Urine Culture

• Amoxicillin-Clavulanic Acid
• Cefixime
• Ceftazidime
• Cefuroxime
• Ciprofloxacin.
• Gentamicin
• Nitrofurantoin
• Ofloxacin
• Nalidixic acid
• Clarithromycin
• Cotrimaxazole
• Cefixime
• Cephalexin
• Cefaclor

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