ISOLATION OF BACTERIA BY DILUTION TECHNIQUES CLINICAL APPLICATION The following

Question

ISOLATION OF BACTERIA BY DILUTION TECHNIQUES CLINICAL APPLICATION The following data were obtained from pour plates used to test the effectiveness of a food preservative. Two sam- samples of the cottage cheese (control) and samples treated with the preservative (experimental) were diluted reservative was added to one sample. After incubation, and plated on nutrient agar. Calculate the number of bacteria. Was the preservative effective? Dilution Amount Plated (m) Number of Colonies CFU/ml Control 1:400 160 Experimental 1:200 0.1 32

Explanation / Answer

The CFU or colony forming unit is a meaure of viable count of bacteria in sample.

It can be calculated by using following formula:

CFU/ml = (number of colonies X dilution factor )/volume of culture on plate

For Control:

The number of colonies = 160

Dilution factor = 400

Volume of culture on plate = 1

CFU/ml = (160X400)/1 = 64000 = 6.4X104

For Experiment:

The number of colonies = 32

Dilution factor = 200

Volume of culture on plate = 0.1

CFU/ml = (32X200)/0.1 = 64000 = 6.4X104

Was the preservative Effective?

Answer: The results of CFU/ml obtained after calculation for both control and experiment indicates that the preservative is ineffective becuase the value of CFU/ml is equal in both cases. By adding the preservative the bacterial count does not decreases.

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