Figure 4

Plaque reduction assay of HSV-1[A] and HSV-2[B] with fraction A, isolated ursolic acid and acyclovir. Different concentrations of fraction A, isolated ursolic acid or acyclovir (5–100 μg/ml) were added to HSV-1 and HSV-2 (black, grey and white bars) infected Vero cells. After 1-2 h incubation at 37°C the cells were overlaid with methylcellulose and the plaques developed after 2–3 days of incubation were stained with crystal violet. The plaque number inhibition was calculated, and the effective concentration of fraction A/isolated ursolic acid that inhibited the number of viral plaques was interpolated from the dose–response curve.