If a 108 dilution contains 48 39 and 69 colonies on 3 sepera

If a 10-8 dilution contains 48, 39, and 69 colonies on 3 seperate plates, calculate the number of CFU/ml of the original culture

Solution

If 10^-8 dilution contains 48 colonies then approx CFU/ml of original culture is 48 x 10⁸ CFU/ml [ as it diluted 10⁸ times]

as same as for 39 colonies plate and 69 colonies plate have 39 x 10⁸ & 69 x 10⁸ CFU/ml respectively.

so to find out no of colonies in original culture we must take an average of these 3 data..

I.e the no. Of CFU/ ml of the original culture is (48+39+69)/3 x 10⁸ = 52 x 10⁸ CFU/ ml.