If you suspect your culture of bacteria has 25 x 107 cells per mL, what would you want the final dilution to be in order to end up with 100 cfu on a plate?

dilution = 2.5*10^6

Explanation:

Given:

- Number of colonies N = 100 cfu

- The Volume of cells = 25*10^7 cells / ml

Find:

the final dilution

Solution:

- The expression relating the the colonies forming unit with cells//volume is given as:

Bacteria/ml = cfu*dilution

dilution = Volumetric cells / cfu

dilution = 25*10^7 / 100

dilution = 2.5*10^6