01 ml of a bacterial culture was pipetted into a 99 ml dilut

0.1 ml of a bacterial culture was pipetted into a 9.9 ml dilution blank. One ml of this dilution was pipetted into a 4 ml dilution blank. 1 ml of this was pipetted into a 9 ml dilution blank. From this dilution 0.2ml wasspread plated onto a TSA plate. 178colonies aroseafter incubation. How many colony-forming units were present per ml of the original culture

Solution

The formula of calculating the CFU is = (no of Colonies formed * dilution) /volume of bacterial cultures plated.

So in first case the dilution factor is 0.1/10 =10^-2.

In second case the dilution factor remains the same ie 10^-2.

In third case the dilution factors become 1/10 =10^-3. So the total dilution factor is 10^-2 *10^-1= 10^-3.

Now the dilution becomes 10^3

According to the forumala (178*10^3)/0.2 = 890 *10^3 CFU/ml..