1. Calculate the CFU/ml of a urine sample if 49 E. coli colonies were counted on NA when 50 microliters were plated on the NA plate from a 10 dilution tube.
1. Calculate the CFU/ml of a urine sample if 49 E. coli colonies were counted on NA when 50 microliters were plated on the NA plate from a 10 dilution tube.
Chapter14: Formula Method
Section: Chapter Questions
Problem 40SST
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Transcribed Image Text:CFU
Remember:
= Number of Colonies Counted x
ml.
1
Dilution Factor
# of ml. plated out
Treat grams dirt or organic material as follows: 1 gram
1 cubic centimeter (1 cm) =1 mL.
%3D
CFU
V;D;=V,D2
OCD =
Volume x Dilution
V=Volume
D=dilution
1. Calculate the CFU/ml of a urine sample if 49 E. coli colonies were counted on NA when 50
microliters were plated on the NA plate from a 10-6 dilution tube.
2. Plating 0.1 mL of a sample diluted by a factor of 10 produced 43 colonies. What was the
original concentration (CFU/ml) in the sample?
3. You have inoculated 100 microliters of a sample diluted by a factor of 103 on a NA plate.
After incubation, you count 58 colonies. What was the original concentration (CFU/ml) in
the sample?
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