Determination of colony forming units 1 ml 1 ml 1 ml 1 ml 1

Determination of colony forming units 1 ml 1 ml 1 ml 1 ml 1 m 1 ml sample of 9 ml 9 ml 9 ml 9 ml 9 ml 9 ml E. coli 1/10 1/100 1/1000 0.1 ml 0.1 ml 0.1 ml 443 63 10-1 10-2 10-3 (colonies Co Calculate CFU/ml

Solution

CFU/ml = (number of colonies* dilution factor)/volume plated (in ml)

= (443 * 10⁴)/0.1 = 4.43 * 10⁵

I have divided by 0.1 because 0.1ml of culture has been plated on the plates to obtain colonies. However, the answer is different if we take 10⁵ and 10⁶ dilutions.

This is the number of bacteria present in one ml of original sample; i.e. the first dilution. (Please note that the first dilution has 1ml of the original sample.)