Detection of antibody to the antiphagocytic factor produced by group E streptococci

Tests for opsonic activity, long chain formation, and precipitins were investigated for ability to detect antibodies to the antiphagocytic factor of group E streptococci. Rabbits, hyperimmunized to serum-grown group E streptococci developed antibodies to the antiphagocytic factor detectable after 2 weeks by the opsonic activity and long chain tests and at 4 to 6 weeks by a precipitin test in which a slide micro double diffusion method was used. Antiphagocytic factor antibodies were dected in swine serums 2 weeks after the swine were experimentally infected, and the antibodies persisted at the end of the experiment at 20 weeks. Demonstration of the antibodies in swine serum was made with the opsonic activity or long chains tests but not with the precipitin test.