Calculte the original concentration of bacteria in the stock

Calculte the original concentration of bacteria in the stock culture.

Given the following dilution scheme, calculate the original concentration of bacteria in the stock culture. Please note the volumes of liquids above the arrows are the transfer volumes from each tube. The volumes under the test tubes are the amount of sterile water before the dilution is made. In this case each dilution black contains 9 ml of sterile water.

Solution

Answer:

6th tube has the dilution factor of 1/10^6 and 65 colonies

Given:

Dilution factor= 1/10^6

Number of colonies= 65

Volume of sample = 1 mL to the plate

CFU/ml = ?

cfu/ml = (no. of colonies)/ dilution factor x volume of culture plate

cfu/ml = (65)/ (1/10^6 x 1)

cfu/ml = 65 x 10^6

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