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Urine culture colony count – Interpretation

Why we should perform Urine culture?

Urinary tract infections are the most common infection type in the world. UTIs infect not only female but also male. Females are most commonly infected because their urethra is short. Urinary tract infections infect by bacteria. Urinary tract infections can be divided into 2 parts. Those are acute uncomplicated urinary tract infections and complicated UTIs. The most common uncomplicated and complicated UTIs causing bacteria is Escherichia coli. Urinary tract infections can be diagnosed using urine culture. In urine culture, CLED is the commonest agar medium. CLED mean Cystine Lactose Electrolyte deficient agar.

If you want more information about CLED agar, watch this video.

Correct specimen types(Correct instruction of patient on how to collect urine is essential)

  • Midstream sample
  • Clean catch sample
  • Supra-pubic aspirate
  • Indwelling catheter

Sample collection bottle should be screw-capped, Wide mouth, and sterile bottle

The procedure of urine culture

  • Mix urine sample well
  • Flame calibrated 0.001ml (1microleter) wire loop and allow it to cool.
  • Insert the wire loop vertically into the urine. Insert only the loop part.
  • Inoculate it on CLED agar medium
  • Inoculate 1/4 plate(9cm plate) or 1/8 plate 14cm plates in an inverted cone-shaped manner.
  • Incubate at 35 Celsius overnight

2nd-day observation

Observe whether there is a growth of colonies on CLED agar or not.
Observe the color of the CLED agar medium. If it is a yellow color, it means Lactose fermenter growth and If it is Blue color, it means Non-lactose fermenter growth on CLED agar.

Urine culture colony count Interpretation reporting procedure

1). Colony count >100

  • interpretation – Pure growth of ≥ 105 CFU/ml
  • ABST – Yes (Yes mean Can be performed)
  • Report *………………. isolated Colony count ≥ 105CFU/ml

2). Colony count >100

  • Interpretation – Mixed growth of 2 organisms with the predominance of one organism (organism 1 ≥ 105 CFU/ml, organism 2 < 104 CFU/ml)
  • Needs discussion with the clinician
  • ABST – ABST for the predominant organism when indicated only
  • Report – Mixed growth with predominant growth of *………………… isolated. Colony count ≥105 CFU/ml
  • Comment – Interpret with clinical details

3). Colony count >100

  • Interpretation – Mixed growth of ≥2 organisms (each >105CFU/ml).
  • ABST – No
  • Report – Heavy mixed growth
  • Comment – Please repeat if clinically indicated

4). Colony count >100

  • Interpretation – Mixed growth with 2 or more types of organisms in catheter samples
  • ABST – No
  • Report – Heavy mixed growth.
  • Comment – Please repeat after removal/ replacement of the catheter

5). Colony count Between 10-99

  • Interpretation – Pure growth of * 104 – 105 CFU/ml
  • ABST – yes
  • Report – 104 – 105 CFU/ml of *………….……. Isolated.
  • Comment – Not necessary

6). Colony count Between 10-99

  • Interpretation – Mixed growth of ≥2 organisms
  • ABST – No
  • Report – Mixed growth
  • Comment – Please repeat if clinically indicated

7). Colony count < 10

  • Interpretation – Any growth < 104 CFU/ml
  • ABST – No
  • Report – No significant growth
  • Comment – Not necessary

8). Colony count – None

  • Interpretation – No growth
  • ABST – No
  • Report – No growth
  • Comment – Not necessary

9). Any growth

  • Interpretation – Any growth taken as significant in suprapubic aspirates, urine taken from the renal pelvis, ureter or bladder during surgery.
  • ABST – Yes
  • Report – Report the isolates with the colony count
  • Comment – Not necessary

Note -Identification of organisms may be important in recurrent infections. Discuss with Microbiologist.

Ushan

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