The relationship between opacity factor and M protein in Streptococcus pyogenes

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Abstract
Lancefield acid extracts of S. pyogenes, type 22 (T12, M22, OF positive) gave good yields of M protein and little opacity factor (OF); sodium dodecyl sulfate extracts contained high titers of OF (> 20,000) and little M protein. Acid-extracted OF could be separated from M protein by Sepharose 4B chromatography; some of the OF-positive fractions that did not precipitate with the absorbed homologous anti-M rabbit serum were able to neutralize opsonic antibodies present in human serum. The isoelectric focusing profiles of the 2 antigens showed partial similarity. Some strains of the OF-positive serotypes, e.g., M-types 22 and 49, lost M antigen and OF activity on serial transfer in Todd-Hewitt broth; this was not seen in a representative of M-type 60; no M-negative, OF-negative variants were detected after 6 subcultures. Among the OF-negative serotypes, some, e.g., M-types 5 and 6, were completely stable; others, e.g., M-types 12, 55 and 57, lost their M antigens after serial subculture. It has been proposed that the genes that code for M antigen are plasmid-borne in some serotypes and are carried on the same plasmid as the gene for OF n some OF-positive serotypes. Analysis of cell lysates by agarose-gel electrophoresis failed to demonstrate the presence of plasmid DNA in any of the strains tested.