Final answer:
To calculate PFU/mL from a plaque assay, count the plaques on an agar plate, adjust for the dilution factor and the plated volume, and multiply to reconstitute the original concentration of the virus in the sample.
Step-by-step explanation:
When you perform a plaque assay to calculate PFU/mL (plaque-forming units per milliliter), you are essentially counting the number of viruses that can infect host cells and form plaques. To calculate PFU/mL from a plaque assay, you must first count the number of plaques on a plate that arose from a known volume of diluted virus. This plaque count is then adjusted by the dilution factor and the volume plated to calculate the concentration of viruses in the original sample.
For instance, if you observe an average of 50 plaques on a plate obtained from a 1:10,000 dilution, and you plated 0.1 mL of the viral suspension, you must consider both the dilution and the plated volume to find the original concentration in the whole sample. The calculation would be 50 (average plaques) × 10 (inverse of volume plated, since 0.1 mL is used, 1 divided by 0.1) × 10,000 (dilution factor), giving a result of 5,000,000 PFU/mL. This figure represents the estimation of the original viral concentration in the sample.