2.57: Exercise 15.3
- Page ID
- 94512
Answer
356,000,000 cells/mL in original sample or 3.56 x 108 cells/mL in original sample
Solution
- # of colonies counted = 89
- amount of diluted sample added to the petri plate in mL = 250 μL = 0.25 mL
- dilution of the petri plate counted = 10-6
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)
(89 colonies) ÷ (0.25 mL diluted sample added to petri plate) = 356 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)
(356 cells/mL in diluted sample) ÷ (10-6 dilution of the petri plate counted) = 356,000,000 cells/mL in original sample or 3.56 x 108 cells/mL in original sample
CFU = 356,000,000 cells/mL in original sample or 3.56 x 108 cells/mL in original sample