Question

You are counting plaques on your plaque assay plates made from serial dilutions of your high titer lysate. Your 10-5 plate has 615 plaques although some are butting up against each other so it is difficult to get an accurate count. Your 10-6 plate has 42 plaques, and your 10-7 plate has only 1 plaque. Which plate would probably yield the most accurate titer calculation of your phage and why is it more trustworthy than the others?

Answer 1

The 10-6 plate that contains 42 plaques will yield most accurate titer calculation. In 10-5 plate, overlapping colonies are present & it will be difficult to count the exact number of colonies present in that plate. Normally plates that contain between 30-300 colonies are considered to be statistically significant. Plates that contain less than 30 colonies can influenced result significantly if small errors in dilution technique or presence of contaminants occur. Plates that have more than 300 colonies, colonies can aggregate & overlap with each other. For these reasons, plates that have less than 30 colonies & have greater than 300 colonies are not consider during plate count technique.