Dilution allows the number of living bacteria to be determined in suspensions that contain even very large numbers of bacteria.

The number of bacteria obtained by dilution of a culture can involve growth of the living bacteria on a solid growth source, the so-called dilution plating technique. The objective of dilution plating is to have growth of the bacteria on the surface of the medium in a form known as a colony. Theoretically each colony arises from a single bacterium. So, a value called the colony-forming unit can be obtained. The acceptable range of colonies that needs to be present is between 30 and 300. If there is less than 30 colonies, the sample has been diluted too much and there is too a great variation in the number of colonies in each milliliter (ml) of the dilution examined. Confidence cannot be placed in the...