FACTORS AFFECTING THE CHAIN LENGTH OF GROUP A STREPTOCOCCI

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Abstract
All strains of group A streptococci studied could be induced to form long chains when grown in the presence of homologous anti-M antibody provided: 1. The strain was rich in M-protein content and 2. The antiserum used was of sufficiently high anti-M titer. With sera of very low anti-M antibody titer, and/or strains containing excessive M-protein content the long chain test became negative. Under such conditions the bactericidal test detected anti-M antibody with greater sensitivity than the long chain test. It was also shown that under appropriate conditions, using minimal antiserum concentrations consistent with a positive test, minute amounts of M-protein could be detected by inhibition of the long chain and bactericidal tests. The amount of M-protein required to inhibit these biological tests was below that which could be demonstrated by conventional capillary precipitin tests.