2.56: Exercise 15.2
- Page ID
- 94511
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Answer
32,400,000 cells/mL in original sample or 3.24 x 107 cells/mL in original sample
Solution
- # of colonies counted = 162
- amount of diluted sample added to the petri plate in mL = 50 μL = 0.05 mL
- dilution of the petri plate counted = 10-4
Step 1: Determine the concentration of cells in the diluted sample:
(# of colonies counted on the petri plate) ÷ (amount of diluted sample added to the petri plate in mL) = CFU in diluted sample (cells/mL)
(162 colonies) ÷ (0.05 mL diluted sample added to petri plate) = 3,240 cells/mL in the diluted sample
Step 2: Determine the concentration of cells in the original sample:
(CFU in diluted sample) ÷ (dilution of the petri plate counted) = CFU in original sample (cells/mL)
(3,240 cells/mL in diluted sample) ÷ (10-4 dilution of the petri plate counted) = 32,400,000 cells/mL in original sample or 3.24 x 107 cells/mL in original sample
CFU = 32,400,000 cells/mL in original sample or 3.24 x 107 cells/mL in original sample