A mutant of Streptococcus mutans 6715 wild type designated C307 has been shown to possess a small amount of either Lancefield- or Rantz-Randall-extractable serotype antigen. Quantitative analysis employing combined immunoabsorption and radial immunodiffusion of anti-S. mutans serotype-specific serum demonstrated that C307 exhibited less than 1% of the amount of serotype g antigen normally expressed in S. mutans 6715 wild type.
