Enhancing Effect of Type Specific Antistreptococcal Antibodies on Emergence of Streptococci Rich in M-Protein.

Streptococci rich in M-protein emerged by natural selection from populations of group A streptococci poor in M-protein during rotation with human blood without homologous type specific antistreptococcal antibodies. When populations of these selected streptococci were then rotated with mixtures of human blood and diluted homologous type specific antistreptococcal rabbit sera, the M-protein content of surviving streptococci was greater, as much as 8-fold, than that of streptococci which survived rotation with human blood alone. In control experiments, when populations of the selected streptococci were rotated with mixtures of human blood and diluted heterologous type specific antistreptococcal rabbit sera, the M-protein content of surviving streptococci was no greater than that of streptococci which survived rotation with human blood alone.