Comparative Studies on Surface Hydrophobicity of Streptococcal Strains of Groups A, B, C, D and G

Abstract

Cell surface hydrophobicity of group A, B, C, D and G streptococcal strains was studied and compared in a new test based on the fact that the degree of bacterial aggregation in (NH4)2SO4 depends on amphiphilic surface antigens. M-positive group A strains showing good growth in normal human blood aggregated in the standard salt aggregation test at very low concentrations of (NH4)2SO4; M-negative strains, which were killed in normal human blood, usually aggregated at high salt concentrations. Agents such as 2 M KSCN, 2 M guanidine HCl or 2 M urea decreased the aggregation of the M-positive strains in the salt aggregation test; nonionic detergents such as Tween 20 (1% wt/vol) and ethylene glycol (2 M) did not affect cell aggregation. Binding of fibrinogen and albumin resulted in a decrease of surface hydrophobicity of the group A M-positive strains. Group B strains possess a hydrophilic surface character and did not aggregate. Group C and G strains behaved in the salt aggregation test like M-negative strains of group A streptococci. Group D strains did not aggregate even at high (NH4)2SO4 concentrations. The results are discussed in relation to the influence of lipoteichoic acid and other surface antigens on strains of the various groups. M protein and possibly other surface protein may contribute to the high surface hydrophobicity of group A strains.