Urine Culture

  


1. Objective

To detect and identify pathogenic bacteria (or fungi) in urine and determine their antibiotic susceptibility, especially in suspected urinary tract infections (UTIs).


2. Principle

Urine is inoculated onto differential and selective media to isolate and identify uro-pathogens such as E. coli, Klebsiella, Proteus, and Enterococcus. A colony count is performed to assess the significance of bacterial growth, and susceptibility testing is carried out using methods like Kirby-Bauer disc diffusion.

 

3. Materials

  • Sterile midstream urine sample

  • Inoculating loop (1 µL or 10 µL calibrated)

  • Culture media:

    • Cystine Lactose Electrolyte Deficient (CLED) agar

    • MacConkey agar

    • Blood agar

  • Incubator (35–37°C)

  • Antibiotic discs (for sensitivity testing)

  • Mueller-Hinton agar (for disc diffusion)

  • PPE and sterile containers

4. Procedure

  1. Mix the urine sample gently.

  1. Use a calibrated loop to streak the urine onto culture media plates (CLED or Blood agar).

  2. Incubate plates at 35–37°C for 18–24 hours.

  1. Count colonies:

    • 1 µL loop → ×1000 = CFU/mL

    • ≥10⁵ CFU/mL = significant bacteriuria

  1. Identify isolates using Gram stain and biochemical tests.

  2. Perform antibiotic sensitivity testing on pure isolates.

5. Result Interpretation

  • Significant bacteriuria: >10⁵ CFU/mL

  • Contaminated sample: Mixed growth of multiple organisms

  • Sterile: No growth

  • Sensitivity report: Lists effective antibiotics with S/I/R interpretation

6. Uses

  • Diagnose UTIs (cystitis, pyelonephritis)

  • Monitor chronic UTI patients

  • Detect asymptomatic bacteriuria (pregnancy, pre-surgery)

  • Guide targeted antibiotic therapy

7. Conclusion

Urine culture is an essential diagnostic test for UTIs. Accurate collection, proper technique, and timely reporting are key to preventing complications and antibiotic misuse.

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