BINDING-PROPERTIES OF STREPTOCOCCUS-SUIS FOR IMMUNOGLOBULIN-G AND OTHER PLASMA-PROTEINS

Immunoglobulin G (IgG) binding proteins on the surface of Streptococcu s suis could be readily detected by direct cultivation of the bacteria on nitrocellulose membranes and subsequent treatment of the membranes with human IgG. Among the 75 S. suis isolates tested two cultures (S. suis P43, S. suis P143) caused a blue colouration of the membranes in dicating IgG binding activities. The Ige binding proteins could be sol ubilized by heat treatment of the bacteria at an acid pH and also by m utanolysin treatment. Western blot analysis revealed numerous protein bands with IgG binding activities. ?he IgG binding proteins were also released into the culture supernatant of the bacteria. This could be d etected for 51 of the 75 S. suis using a microfiltration assay. In bin ding studies with I-125-IgG S. suis P43 and S. suis P143 but none of t he other S. suis isolates showed a significant binding of the protein. These two cultures additionally bound I-125-albumin, I-125-alpha(2)-m acroglobulin and I-125-fibrinogen all from humans but not I-125-chicke n IgG or I-125 human haptoglobin 2-1. The binding profiles of the two S. suis cultures rested indicate a close relation of these binding pro teins with streptococcal protein G.