Isolation of an (O,H,Vi)-free immunoprotective antigenic fraction with mannose receptor-like activity from Salmonella typhi.

An antigenic fraction of Salmonella typhi strain TY6S, obtained from a bacterial pellet by washings with 1.5 M NaCl and ultracentrifugation in a 5%-20% sucrose density gradient, induced serum antibodies in rabbits that protected chicken embryos challenged with lethal doses of the virulent microorganism. The antigenic preparation was free of Vi, O, and H antigens. It contained about 85% protein and Rd1P+ lipopolysaccharide. The protein moiety comprised three polypeptides of 45,000, 32,000, and 20,000 daltons, respectively. In addition, the purified preparation exhibited the properties of a bacterial adhesin with receptor-like activity for mannosyl residues, as shown by agglutination of target cells containing these residues at their surfaces.