Bacterial adherence: the attachment of group A streptococci to mucosal surfaces

It is now recognized that bacteria bind to and colonize mucosal surfaces in a highly selective manner. After the organisms penetrate the nonspecific mechanical and cleansing forces, ligands (or adhesins) on the surface of the bacteria interact in a lock-and-key (or induced-fit) fashion with complementary receptors on mucosal surfaces of the host. The adhesins are usually composed of proteins in the form of fimbriae or fibrillae and the receptors of glycolipids or glycoproteins. In group A streptococci the adhesin, lipoteichoic acid (LTA), is anchored to one or more proteins on the surface of the bacterial cells and interacts through its lipid moiety with fibronectin molecules deposited on and bound to the epithelial cells. In an attempt to locate the region of fibronectin recognized by LTA and group A streptococci, fibronectin was cleaved with thermolysin and the fragment mixture adsorbed with Staphylococcus aureus or Streptococcus pyogenes. Staphylococci adsorbed several high-molecular-weight fragments as well as a 28-kilodalton and a 23-kilodalton fragment, whereas S. pyogenes cells adsorbed only the 28-kilodalton fragment completely. The adsorption of the fragments by S. pyogenes was blocked by LTA. Antibodies raised against a synthetic peptide copying the NH2 terminus of fibronectin reacted in a western blot with the 28-kilodalton fragment; this result indicated that S. pyogenes and its LTA react with the NH2-terminal region of fibronectin at a site distinct from that at which S. aureus reacts. Our findings are consistent with the idea that LTA mediates the attachment of group A streptococci to fatty acid binding sites of fibronectin deposited on mucosal epithelial cells.