Question

You want to establish a synchronous infection by a virus of a culture that contains 100,000 HeLa cells. You have a virus sample whose concentration you have just determined by doing a plaque assay. The results of the plaque assay in which you tested 1 ml of each of the indicated diolutions are shown below (cells are stained with crystal violet). How many ml of your undiluted virus sample do you need to put onto the HeLa cells to start your infection?

1:1000 1:10,000 1:100,000 1:1,000,000 1:10,000,000 1:100,000,000

1.0 ml

0.2 ml

0.05 ml

0.025 ml

Answer 1

The undiluted sample will be depends upon the titre value of the serial diluted plaque assay. In this case the plaque assay is used to isolate the virus by the infection of host the concentration of the virus is calculated by the plaque forming unit

.PFU= Total number of virus used for the infection/total number of HELA cells.

Based upon the values generally we will count 100 plaques only for minimizing error .Taking upon the dilution factor into consideration and based upon the results the 0.025 ml is optimal ml required for starting infection.

NOTE: 1;100,000 is the 0.001% in solution.