Viability of HAdV-3p E3-9K mutant virus-infected A549 cells. A. A549 cells were infected with HAdV-3p E3-9K mutant viruses at a MOI of 10 PFU/cell. Medium and trypsinized cells were pooled at indicated times pi, stained with an equal volume of 0.4% trypan blue solution, and approximately 200 cells were counted using a light microscope and hemocytometer. The percentage of viable cells was determined by dividing the number of unstained cells by the total number of cells counted. Error bars indicate standard error of the mean for three independent experiments. Mock-infected cells were used as a negative control. B. HAdV-C rec 700 and pm734.1 controls. Representative trypan blue exclusion assay results consistent with those reported by Tollefson et al. for the same viruses.