Question

Case 1

Patient with suspected UTI infection

You are working in microbiology core lab facility and you receive a urine sample from patient X. Your responsibility is to establish whether the patient is suffering from a UTI infection.

CFU/ml < 10³ / ml urineà no infection

CFU/ml >10⁵ / ml urineà Yes for infection

You are asked to conduct a 6 serial dilutions of the original urine sample (dilution is based on 1 /10ml ) and plating 1 ml from each dilution on a nutrient agar.

Your result show that the plate from dilution 5 had 46 CFUs.

1- Calculate the original number of CFU/ml in urine sample and

2- Indicate whether the patient has a UTI infection or not.

Answer 1

ANSWER 1
Dilution 5 would have 10⁵ level of dilution.
The plating would have introduced a further 10 dilution.
So, now we have a 10⁶ dilution.
= 46 * 10⁶ CFU/mL

ANSWER 2
The patient has a UTI infection, since the given value is more than 10⁵ CFU / mL