Define Plate Counts and Colony Forming Unit?

Plate counts is the most frequently used method to measure microbial numbers. The technique, however, can be used only for those microorganisms, which are able to grow and reproduce on microbial media. Here a diluted sample of microbes is dispersed over suitable nutrient agar medium. There are two ways of performing a plate count - the spread plate and pour plate technique about which we have already studied in the last practical. Look up these techniques once again. Each microorganism then produces a distinct colony. Original number of viable microorganism in a sample is then calculated from the number of colonies formed and the sample dilution used. The results are reported in form of colony forming units (CFU) per ml of the sample.

Colony forming unit/ml can be expressed as:

CFU/ml = (No. of colonies formed * dilution factor) / Volume Sampled