Question

A 1/20 serial dilution of a bacterial culture was performed in tubes "A" through "E" starting with tube "A" and proceeding to tube "E". 100 microliters of the diluted culture from the final tube "E" was spread onto a plate. Following incubation of the plate, growth of the bacteria produced 50 colonies on that plate. What is the concentration of viable cells in tube "B" (in cells per milliliter)? (2 pts)

Answer 1

Answer: The answer is 8x10^7 cells per milliliter

Explanation: In the series of dilution, you are dividing by 20 for every tube. There is a total of 5 tubes the last one being 6.25x10^-6. If 50 colonies are in 100 microliters, it is the same to say that there are 500 colonies in 1 milliliter. Divide the value of 500 by 6.25x10^-6 to find the concentration in of cells in 1 millilter.