A student prepares a dilution series of a bacterial culture

A student prepares a dilution series of a bacterial culture. (Dilutions series are a 1/10 dilution.) They plate

0.10 ml from each tube in the on separate agar plates. After incubation, 300 colonies were observed on the

fourth plate in the dilution series. What was the concentration of viable cells in the original culture?

Solution

The dilution series are a 1/10 dilution. Therefore, dilution factor of the 4^th plate DF = 10⁴.

Number of colonies formed on the 4^th plate N = 300

Volume of culture plated V = 0.10 ml

Then, the concentration of original plate will be C = N x DF/ V = 300 x 10⁴ /0.1 = 3 x 10⁷ /ml.

Therefore, the concentration of viable cells in the original culture is 3 x 10⁷ /ml.