The serum opacity reaction of Streptococcus pyogenes: frequency of production of streptococcal lipoproteinase by strains of different serological types and the relationship to M protein production

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Abstract
SUMMARY: The serum opacity reaction (SOR) is produced by some streptococci of group A, but not by streptococci of groups B, C, D, F and G. The production of this reaction was found to be closely related to serotype as determined by M and T antigens. The SOR of an individual strain was found to be consistently stable over a period of time both in strains maintained in the laboratory and in strains isolated sequentially from individual patients following streptococcal infections. Strains for which the demonstration of an M-antigen by the precipitin method was difficult or impossible in general produced a SOR, while strains more easily typable generally failed to produce this reaction. Laboratory selected variants of type 12 strains showed an inverse relationship between M protein and lipoproteinase production, whereas M positive and M negative variants of other serotypes showed no variability with respect to lipoproteinase production.