02 ml of a 108 dilution of a bacterial suspension plated on

0.2 ml of a 10^-8 dilution of a bacterial suspension plated on an agar plate gave rise to 135 distinct colonies. What is the concentration (CFU/ml) of bacteria in the original, undiluted suspension?

Solution

Colony forming unit (CFU) is a measurement of viable microorganism like bacterial or fungal cells. Actually it is a bacteria or fungi that is capable to form a group of the same microorganism by reproducing.

Colony forming unit per milliliter (CFU/ ml) can be calculated by using the formula:

CFU/ ml= (No. of colonies _* Dilution factor) / Volume of the culture plate

In the question given dilution is 10^-8 then dilution factor will be 10^8

Volume of culture plate = 0.2ml

No. of colonies = 135

By putting the value in the formula,

CFU/ ml= ( 135 _* 10^8) / 0.2

CFU/ ml= 675 _* 10^8 = 6.75 _* 10^10

CFU/ ml= 6.75 _* 10^10

So total Colony forming unit (CFU) = 6.75 _* 10^10 CFU/ ml