A stock sample of phage is diluted 110 one time and then dil

A stock sample of phage is diluted 1/10 one time and then diluted 1/1000 twice. A 0.1-mL portion of the final dilution is transferred to a test tube that contains 0.3 mL of E. coli cells and 4 mL of molten agar. The tube’s contents is mixed well and poured onto a Petri dish of solid agar medium. After an overnight incubation, 158 plaques appear on the plate. What is the concentration of phage in the stock sample?

Solution

Answer:

Dilution factor = 1/10 x 1/1000 x 1/1000 x 1/10= 1/10^7

Given:

Dilution factor= 1/10^7

Number of colonies= 158

Volume of sample = 0.1 mL to the plate

CFU/ml = ?

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

cfu/ml = (158)/ (1/10^7 x 0.1)

cfu/ml = 158 x 10^8

concentration of phage in the stock sample = 158 x 10^8/mL