Suppose you spread a plate to enumerate the cell concentration of an E.coli cult

Question

Suppose you spread a plate to enumerate the cell concentration of an E.coli culture. You make a series of dilution 1/10, 1/100, 1/1000, 1/10000, 1/100000 and take 0.1ml to spread. The plate from 1/10 dilution grow into a lawn of connected colonies, not possible to count the number. The number of colonies counted from the other four spread-plates are 800, 289, 25, and 3 respectively. What is the cell concentration of the original E.coli culture? 8 x 105 cells/ml 3 x 106 cells/ml 2.89 x 106 cells/ml 2.5 x 106 cells/ml Not enough information to calculate the concentration Submi Answer Tries 0/99 This discussinn is closed

Explanation / Answer

Ans. Formula used to calculate the the CFU is:

CFU=No.of colonies formed/Volume plated * dilution factor

1. If we take the dilution factor 1/100

CFU=800/0.1*1/100=8X105 cells/ml

2. If we take the dilution factor 1/1000

CFU =289/0.1*1/1000=2.89X106 cells/ml

3. If we take the dilution factor 1/10000

CFU=25/0.1*1/10000=2.5 X 106 cells/ml

4. If we take the dilution factor 1/100000

CFU=3/0.1*1/100000=3 X 106 cells/ml

So, the information is not appropriate to calculate the concentration.

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