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Biology Lab - Serial Dilutions and CFUs

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One mL of yogurt was added to 99mL sterile diluent. Decimal (1/10) dilutionswere then made, and one-tenth mL was plated in duplicate on plate count agar. After incubation, the following colony counts were made:

Dilution colony count using the data, calculate the # of cfu's per gram of the yogurt (1mL of yogurt = 0.4g)

initial dilution TNTC, TNTC
First 1/10 dilution TNTC, TNTC
2nd 1/10 dilution 412, 422
3rd 1/10 dilution 54, 56
4th i/10 dilution 6, 4

I tried to do this but don't know - Ex. on dilution 3 -
412 +422= 834/2 =417 417/0.1 X 10^2 = 4.17x10^5


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Solution Preview

Hi there,

almost right! Off by one decimal, and forgot to transform to grams. Think about it: The first dilution 1ml was added to 99ml diluent (so a 1:100 dilution), next a 1:10 dilution and then ...

Solution Summary

Serial dilutions and CFUs for a biology lab is examined.