FIG. 1.

The 12-S3 variant is compromised for growth in culture. (A) MDCK cells were infected with the wild-type A/Victoria/3/75 virus, the 12-B1 variant, or the 12-S3 variant in a standard plaque assay. After 3 days at 37°C, the cell monolayers were stained to reveal the size of the plaques. (B) MDCK cells were infected with the wild-type virus or the 12-S3 variant at a multiplicity of infection of 0.001 PFU per cell. At the indicated times after infection, the titer of virus in the culture supernatant was determined. The data points are means and standard deviations obtained from duplicate wells in a representative experiment.