In a plaque assay, a microbiologist counts 20 plaques on a plate. How many plaque-forming units can be assumed to have been present in the original bacterium-virus mixture on the plate if there was no dilution of the mixture prior to plating

20

Explanation:

Viral plaque assays determine the number of plaque-forming units (pfu) in a virus sample, which is one measure of virus quantity. This assay is based on a microbiological method conducted in Petri dishes or multi-well plates.

If there was no dilution of the bacterium-virus mixture, there will be 20 plaque-forming units that are what microbiologist counts on the plate.