Plaque purification of the recombinant HSV-1. (a) First round of infection shows the presence of green plaque of recombinant HSV-1 surrounded by the plaques of regular HSV-1 BAC virus. (b) Second round of plaque purification was performed by collecting the plaque from round one followed by infecting fresh Vero cells in a dilution of 1 : 20. Decrease in the background by regular HSV-1 BAC virus can be seen. (c) Third round of plaque purification was done by repeating the round 2 and showed no background by the regular HSV-1 BAC virus.