FIG. 7.

Effect of trypsin pretreatment on growth of PI viruses in cured MX cells. Monolayer cultures of MX-S cells (10⁵ cells) were infected with PI-SA11-B/135 and PI-SA11-D/128 at an MOI of 2 PFU per cell. Prior to adsorption, each viral inoculum was either untreated or treated with 10 μg of trypsin per ml at 37°C for 30 min. After 1 h of adsorption, the inoculum was removed, 1.0 ml of fresh trypsinfree medium was added, and cells were incubated at 37°C for 24 h. Virus in cell lysates was titrated by plaque assay using MA104 cells. The results are presented as the mean viral yields (titer at 24 h divided by titer at 0 h) for four independent experiments. Error bars indicate standard deviations of the means.