The Adherence of Group A Streptococci to Oropharyngeal Cells: the Lipoteichoic Acid Adhesin and Fibronectin Receptor

The attachment of group A streptococci to oropharyngeal epithelial cells is mediated by adhesive molecules (adhesins) on the surfaces of the micro-organisms that interact with receptor molecules on the epithelial cells. The evidence that the adhesin is composed of lipoteichoic acid (LTA) complexed with bacterial cell surface proteins is as follows: (a) Among the purified cell wall substances tested, only LTA was able to inhibit attachment; (b) treatment of streptococci with anti LTA but not with antibody against other surface substances blocks attachment; (c) LTa forms complexes with purified M protein, the most abundant protein on the surface of virulent streptococci; (d) the lipid moieties of LTA, which mediate attachment, remain free in the M protein-LTA complexes to interact with receptor analogues, such as serum albumin. The evidence that the receptor for the LTA mediated binding of streptococci resides in fibronectin molecules on oropharyngeal cells is as follows: (a) the addition ot adhesion test mixtures of fibronection inhibits binding; (b) the number of streptococci capable of attaching is directly proportional to the amount of fibronectin present on epithelial cells; (c) purified fibronectin immobilized on latex beads agglutinates suspensions of streptococci; (d) radiolabeled fibronectin binds to group A streptococci; (e) both the agglutination of fibronectin-beads and the binding of fibronectin to streptococci is blocked by LTA, the streptococcal adhesin.