1.) In order to determine the cfu/ml of bacteria in a milk sample, you dilute 1

Question

1.) In order to determine the cfu/ml of bacteria in a milk sample, you dilute 1 ml into 9 mls of sterile water and label it tube A. From tube A, you transfer 1 ml into a new tube containing 9 mls of sterile water (tube B). From tube B, you transfer 1 ml into a new tube containing 9 mls of sterile water (tube C). From tube C, you transfer 1ml into a new tube containing 9 mls of sterile water (tube D). Then, you plate 100 microliters( dilution onto nutrient agar. On the plates from tube D, you counted 50 colonies. What is the cfu/ml of bacteria in your milk sample? Show your work and use scientific notation. 0.1 ml) of each

Explanation / Answer

CFU/ml = n/s*d

Where n= number of colonies

S = Volume of sample plated

D = dilution factor.

Dilution factor here is 10-4

Sample plated is 0.1 ml

Colonies counted are 50.

So 50/0.1*10-4

So, 50 x 105 is the cfu/ml.

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