How do I analyze the result of the pour plate method?

Following the incubation period, one should inspect the plates for visible colonies. Similar-looking colonies typically indicate the presence of single bacterial species, while diverse colony appearances suggest multiple species or potential contamination. To calculate the CFU/mL, the following formula should be used:  

CFU/mL= Total number of colonies * dilution factor/volume of sample used (aliquot)

The optimal colony count should fall between 20-300 CFU/mL. Counts above or below this range may require to repeat the procedure for more accurate results.