2.55: Exercise 15.1
- Page ID
- 94510
Answer
211,000,000,000 cells/mL in original sample or 2.11 x 1011 cells/mL in original sample
Solution
- # of colonies counted = 211
- amount of diluted sample added to the petri plate in mL = 100 μL = 0.1 mL
- dilution of the petri plate counted = 10-8
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)
(211 colonies) ÷ (0.1 mL diluted sample added to petri plate) = 2,110 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)
(2,110 cells/mL in diluted sample) ÷ (10-8 dilution of the petri plate counted) = 211,000,000,000 cells/mL in original sample = 2.11 x 1011 cells/mL in original sample
CFU = 211,000,000,000 cells/mL in original sample or 2.11 x 1011 cells/mL in original sample