Plating 10 mL of a sample diluted by a factor of 103 produce

Plating 1.0 mL of a sample diluted by a factor of 10^-3 produced 43 colonies. What was the original cell density in the sample? Plating 0.1 mL of a sample diluted by a factor of 10^-3 produced 43 colonies. What was the original cell density m the sample?

Solution

11).

Given that the number of colonies formed after dilution = 43

Dilution is = 1 ml of a 10^-3 dilution

In initial concentration, plaque forming units /ml (CFU/ml) = Number of colonies/ dilution * volume of diluted virus added to the plate = 43/ 1* 10^-3 = 43* 10^3 CFU/ml.