A haemagglutinating adhesin of group B streptococci isolated from cases of bovine mastitis mediates adherence to HeLa cells

Abstract

Rabbit erythrocytes were agglutinated by 43.4% of group B streptococci isolated from bovines but by none isolated from humans. Haemagglutination was enhanced by cultivation of the bacteria under microaerophilic conditions. Most of the haemagglutinating strains had protein type antigen X, either alone, or in combination with polysaccharide antigens. Heat and proteolytic treatment of the bacteria destroyed the haemagglutination activity. The haemagglutinin could be solubilized from the bacterial surface by mutanolysin treatment and isolated from culture supernatant fluid by ammonium sulphate precipitation. The isolated haemagglutinin did not cause direct agglutination of erythrocytes. However, binding of the haemagglutinin to rabbit erythrocytes could be visualized by agglutination of haemagglutinin-treated erythrocytes by specific antiserum obtained by absorption. Western blotting showed that the haemagglutinin obtained from erythrocyte lysates contained an antibody-reactive band with a molecular mass of 43 kDa. Haemagglutination-positive strains adhered to HeLa cells in higher numbers than did haemagglutination-negative strains. The HeLa cell adherence of Group B streptococci was inhibited in the presence of isolated haemagglutinin or of specific antiserum against the haemagglutinin. These observations suggest that the haemagglutinating adhesins of bovine group B streptococcal isolates are directly involved in the adherence mechanisms of these organisms.