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Taylor, a MIC 206 student needs to determine the OCD of a sample of Escherichia coli. She performed dilutions using four 9 ml dilution blanks and plated 1.0 ml from the final dilution tube. 137 colonies grew on the plate. Calculate the number of CFU/ml that should be present in the original E. Coli sample.

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Answer:

1.37 x [tex]10^6[/tex] CFU/mL

Explanation:

First, the dilution factor needs to be calculated.

Since four 9 ml dilution blanks were prepared, the dilution factor that yielded 137 colonies is of [tex]10^{-4}[/tex].

Next is to divide the colony forming unit from the dilution by the dilution factor:

   137/[tex]10^{-4}[/tex] = 137 x [tex]10^4[/tex]

In order to get the CFU/ml, divide the CFU from the dilution by the plated volume (1 mL) from the final dilution tube.

   137 x [tex]10^4[/tex]/1 = 1.37 x [tex]10^6[/tex]

Hence, the CFU/ml present in the original E. coli sample is 1.37 x [tex]10^6[/tex].

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

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