Comparison of the phenotype of wild-type YK304 and the recombinant viruses MT102 and MT103. (A) Vero cells were infected with YK304 (filled circles), MT102 (open triangles), or MT103 (open circles) at a multiplicity of 3 (thick lines) or 0.01 (thin lines) PFU per cell. The supernatants and cells were harvested at the indicated time points, and cell lysates were titrated on Vero cells. (B) Photographs of plaque produced by wild-type YK304 (left panel), MT102 (middle panel), and MT103 (right panel). Vero cells infected with each of the recombinant viruses at an MOI of 0.0001 PFU per cell under plaque assay conditions. Phase-contrast photographs were recorded 2 days after infection. (C) The mean diameters of 20 single plaques per recombinant virus were determined.