Fibrinogen Binding Structures in Beta-hemolytic Streptococci Group A, C, and G. Comparisons with Receptors for IgG and Aggregated Beta 2-microglobulin

Binding of radiolabelled fibrinogen was measured to 197 strains of 16 different bacterial species. All streptococcal strains belonging to groups A, C, and G isolated from human sources were strongly positive. S. aureus strains showed low binding values. Occasional group B streptococci were positive. Reactive strains were also noted among group C streptococci of animal origin, Streptococcus zooepidemicus and Str. equii, and bovine beta-hemolytic group G streptococci. Bovine alpha-hemolytic group G strains as well as the remaining seven species of human origin were all negative. Inhibition experiments and correlation studies indicated that the streptococcal receptor for fibrinogen was different from immunoglobulin Fc binding reactivity. Comparisons with the newly discovered beta 2-microglobulin binding factor showed that trypsin concentrations which destroyed this receptor left the fibrinogen receptor intact. Although the two receptors correlate in strain population studies and show competition for binding the difference in trypsin sensitivity indicates that they represent two different structural entities. Both receptors might serve as basic markers for M-protein like surface components of Gram positive cocci.