Introductory Microbiology

Methods of determining growth

• A variety of direct as well as indirect methods are available to determine growth and growth rates of microorganism. The direct methods involve determining the increase in cell number, dry weight or the increase in any other cellular component as a function of time while indirect methods include measurement of optical density, turbidity etc.
• The total number of cells in a population can be determined either microscopically or electronically. In the microscopic method, the number of cells are determined by haemocytometer, by the dilution plating technique.
• Other direct methods of estimating growth include the estimation of cell nitrogen or increase in cell dry weight or any other cellular components. For determining the dry weight, the culture is centrifuged in pre weighed tubes and the pellet is dried to constant weight at 80º-850C.
• The most popular indirect method of determining growth in bacteria or yeast is by the use of colorimeters or turbidometers in which, the density of the cell suspension can be determined.