The relationship between opacity factor and M protein in Streptococcus pyogenes.

Lancefield acid extracts of Streptococcus pyogenes, type 22 (T12, M22, OF positive) gave good yields of M protein and little opacity factor (OF), but sodium dodecyl sulphate (SDS) extracts contained high titres of OF (greater than 20000) and little M protein. Acid-extracted OF could be separated from M protein by Sepharose 4B chromatography, but some of the OF-positive fractions that did not precipitate with the absorbed homologous anti-M rabbit serum, were able to neutralise opsonic antibodies present in human serum. The isoelectric-focusing profiles of the two antigens showed partial similarity. Some strains of the OF-positive serotypes, e.g., M-types 22 and 49, lost both M antigen and OF activity on serial transfer in Todd-Hewitt broth, but this was not seen in a representative of M-type 60, and no M-negative OF-negative variants could be detected after six subcultures. Among the OF-negative serotypes some, e.g., M-types 5 and 6, were completely stable, whereas others, e.g., M-types 12, 55 and 57, lost their M antigens after serial subculture. One explanation is that the genes that code for M antigen are plasmid borne in some serotypes and, moreover, are carried on the same plasmid as the gene for OF in some OF-positive serotypes. However, analysis of cell lysates by agarose-gel electrophoresis failed to demonstrate the presence of plasmid DNA in any of the strains tested.