Question

1. Suppose that you carry out a urine culture for each of the given samples. Calculate the CFU for each of the samples. If a CFU can not be determined explain why this can not be determined. List an additional test or media that can be used to further identify the possible pathogenic organism. NOTE 56 µl was used for each sample
   1. You obtain a sample from a patient, the estimated concentration of the bacteria is 10⁸, after 24 hours the colony count is 256. Following the incubation you run a Gram Stain and you notice it is Gram Negative. What media can be used to determine if the organism is E.coli what would the expected result be?

2. Sample B contains an estimated concentration of 10⁴ , After 24 hours of incubation you obtain a colony count of 89. You also notice beta hemolysis is dominant, based on the test we have conducted in lab what organism is most likely organism that this bacteria can be? How would you confirm this organism (note that there is more than one test to confirm this)  

Answer 1

Ans: Firstly, CFU  is a measure of viable bacterial or fungal cells.In direct microscopic counts i.e. cell counting using haemocytometer,where all cells- dead and living, are counted,but CFU measures only viable cells. For benefit or ease  the results are given as CFU/mL for liquids .CFU can be calculated using miles and misra method.

The CFU/ml can be calculated using the formula:

cfu/ml = (no. of colonies x dilution factor) / volume of culture plate.