Characterization and mixed infections of three strains of vaccinia virus: Wild type, IBT resistant and IBT dependent mutants

The characteristics of IBT dependent (IBT(D)) and IBT resistant (IBT(R)) mutants of vaccinia virus were compared with those of the wild type (wt) strain. The mutants did not differ from the wild type strain by their sedimentation in sucrose gradients. Minor differences in the polypeptide composition of the virus particles and in the neutralization of the three virus strains by anti vaccinia human immunoglobulin were observed. Mixed infections of the viruses in HeLa cells enabled the growth of the strains under their unfavourable conditions (wt in the presence of IBT and IBT(D) in the absence of IBT).