Type-specific antigen of Streptococcus rattus strains (KAY1 and FA1). I. Characterization

A serotype-specific antigen was extracted from Streptococcus rattus KAY1 strain isolated first in Japan from human dental plaque and purified on an ion exchange column to compare it chemically and immunologically with that of FA1 strain which had been examined extensively by previous workers. Antigens of both strains reacted in a double diffusion test specifically with anti-FA1 serum which had previously been demonstrated specific for the strains in the same test, agglutination reactions and/or radioimmunoassay using whole cells. After separation on a DEAE-Sephadex A-25 ion exchange column the antigen was found to be resistant to various enzymatic treatments with pronases, lipase and nucleases and produce a single precipitin band against absorbed anti-FA1 serum in immunoelectrophoresis. Chemical analysis of this antigen revealed that it composed of carbohydrate, protein and a few percentages of glycerol and phosphorus. Hapten inhibition tests between antigen and antibody showed that galactose as well as glucose were the most potent inhibitors, suggesting their involvement in the antigenic determinant. Involvement of the sugars was also supported by gas chromatographic analysis and abolishment of reactivity with antiserum after the treatment of antigens with NaIO4. Moreover, protein does not seem to be involved since after SDS-PAGE analysis an enzyme immunoassay gave a negative reaction with immunoblotted antigens.