If 0150 mL of 1075 dilution yielded an average of 256 coloni

If 0.150 mL of 10^-7.5 dilution yielded an average of 256 colonies/plate, calculate the number of bacteria per mL of the original culture. Show all calculations.

Solution

The number of colony-forming units (CFU) = [no of cells]/ [volume of dilution x volume of diluted sample added to the plate]

Now CFU per ml of dilution is 256 colonies divided by 0.150 ml plated = 1706.7 colony-forming units/ml of dilution.

Dividing this number by the 10^-7.5 dilution = 1706.7 / 10^-7.5 = 1706.7 x 10^7.5 colony-forming units/ml of original culture sample