1. Viable plate count The most common method of estimating bacterial growth which involves counting the number of bacterial colonies grown on solid media after incubation of the inoculated media for 18-24 hours.
The sample is serially diluted.
The suspension is inoculated on solid media by surface spread technique i.e. the suspension is spread
The plate is incubated for 18-24 hrs to allow the bacteria to grow and form colonies.
The concentration of bacteria in the original sample can be determined by counting the visible colonies multiplied by the dilution factor.
Number of colonies =Number of colonies Χ dilution factor
Volume of sample NB: The statistically significant plate count is between 30 and 300 colonies. Less than 30 colonies on a plate are not accepted for statistical reasons. Greater than 300 colonies on a plate are too close to distinguish as an individual colony forming unit (too numerous to count). Limitation of viable plate count: It selectively in favor of a certain group of bacterial population.