Introduction Many of our genetic understandings of biological processes have been determined by either studying the processes in bacteria or by using bacteria to isolate and study genes from other organisms. A basic aspect of such genetic analysis is the ability to quantify the number of bacteria in a cell culture.
Most bacteria are able grow in liquid culture media and on a solid agar surface.
Cell counts can be made of bacteria growing on both. In liquid culture, bacteria produce colloidal suspensions that can inhibit light passing through it. The concentration of cells in the culture is directly proportional to the optical density or absorbance of light by the culture. Turbidimetry allows measurement of the percentage of light absorption and thus of the cell concentration of a culture. Quantitative plate counts are a more accurate, but time consuming, method of determining the cell concentration of a culture.