Index >> Growth of Microorganism >> Methods of Determining Microorganisms Growth

In these methods, a known amount of medium (in multiples) is inoculated with a known number of spores or cells and incubated. At lated one or more flasks are withdrawn and the cell mass is collected by cent ifugation. If centrifuged in a graduated conical glass tube, the direct packed volume of the cell pellet can be determined. For determining the dry weight. The culture is centrifuged in preweighed tubes and the pellet dried to constant weight at 80-85°C.
The most popular indirect method of determining growth in bacteria or yeast is by the use of  colorimeters or turbidometers in which density of the cell suspension can be determined. By taking adequate the precautions, the method can be made reliable and useful. The type of curves that one gets when growth is measured hi a liquid medium by different methods. The changes that occur in the cell population after inoculation into fresh growth medium are more correctly indicated by the dry weight or optical density measurements. In the lag period, as said earlier, biosynthetic activity leading to increase in mass occurs but this cannot be identified if the cell number is determined.