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A new type of surface receptor for serum albumin was detected in strains of Streptococcus pyogenes (group A). This receptor, called type e, was different from albumin receptors in other streptococcal species. Only mouse and human serum albumin was bound to the receptor. The albumin-binding capacity was high: 2 X 10(8) bacterial organisms bound 11 micrograms of mouse albumin. The receptor was stable even when treated at 100 degrees C for 5 min. Binding of albumin was not mediated by lipoteichoic acid (LTA) because of lack of correlation to surface LTA, restricted albumin reactivity, and positive binding in presence of 2% Tween 20. Presence of albumin receptor type e correlated to presence of M-protein as measured by growth in the bactericidal test. All 51 M-protein positive group A streptococcal strains tested could bind mouse albumin whereas only 3 out of 8 M-protein negative strains showed positive binding (P less than 0.001). The sensitivity to trypsin digestion suggests that the albumin receptor is of protein nature or mediated by a protein.

Twenty M protein-positive and eight M protein-negative strains of group A streptococci were investigated with respect to surface hydrophobicity and amount of lipoteichoic acid (LTA). Surface hydrophobicity as determined in polymer two-phase systems varied substantially between individual strains and there was no correlation to the presence of antiphagocytic M protein. The amount of LTA on the surface of the bacteria varied with hydrophobic affinity of the cells. Strains with a high content of surface LTA were found among both M-positive and M-negative streptococci. Cellular and extracellular LTA was estimated on six strains by the ability of hot phenol extracts and culture fluids to sensitize erythrocytes and by rocket immunoelectrophoretic quantitation. Differences in content of surface LTA did not correlate to differences in the total amount of cellular LTA. Pepsin digestion of M-positive group A streptococci at suboptimal pH resulted in a loss of M antigen whereas surface LTA and the hydrophobic interaction liability was retained. The results indicate that the degree of surface hydrophobicity as measured by two-phase partitioning is not correlated to either the type-specific or the antiphagocytic moiety of M protein. The results support the correlation between surface LTA and surface hydrophobicity of group A streptococci.