Question

What is the concentration of cells in the starting sample if 1 ml was plated per dilution and the starting sample was river water?

Report your answer below as a decimal with one significant digit after the decimal and report the exponent the separate box. See this example, if your answer is 5.2 x 10⁸ you would report it as "5.2"

You have the following results from a serial dilution experiment: Sample Dilution Plate Count 1:101 Too many to count 1:102 Too many to count 1:103 Too many to count 1:104 287 1:105 15 1:106 1:107 What is the concentration of cells in the starting sample if 1 ml was plated per dilution and the starting sample was river water? Report your answer below as a decimal with one significant digit after the decimal and report the exponent the separate box. See this example, if your answer is 5.2 x 108 you would report it as "5.2" in the first box and "8" in the second box. Concentration = x 101 cells/ml

Answer 1

CFU/mL= number of colonies/ ( volume plated in mL$\times$ dilution)

dilution= 1/10^-4

number of colonies in the range of 30- 300 is used for the CFU/ mL calculation, here for dilution 1:10^4 the number of colonies=287

volume plated=1 mL

CFU/mL= 287/(1$\times$10^-4)

= 2.87$\times$10^6 /mL

concentration= 2.87$\times$10^6 cells/mL