Bacteriostatic effect of serum: role of antibody to lipopolysaccharide.

Previous work has shown that antibody and transferrin, acting together, exert a bacteriostatic effect on certain pathogenic Escherichia coli. This effect may be due to the ability of the antibody to interfere with the release of the iron chelator, enterochelin, from the bacterial cell. Enterochelin is essential for the transport of iron from transferrin to the bacterial cell. The nature of the bacterial antigen against which the antibody is directed has now been determined by means of adsorption experiments. It was found that absorption of serum either with hear-killed cells of E. coli O111 or with Boivin antigen abolished the bacteriostatic effect. A monosaccharide, which proved to be colitose (3,6-dideoxy-L-galactose), was isolated after acetic acid hydrolysis of the Boivin antigen. Colitose is the terminal monosaccharide of the O-specific side chain of the lipopolysaccharide from E. coli O111. This monosaccharide abolished the bacteriostatic effect of both whole serum and mixtures of antibody and iron-binding proteins. When administered by the intraperitoneal route, it reduced the resistance of mice to subsequent infection with E. coli O111. This ability of colitose to interfere with antibacterial mechanisms is in accord with published immunochemical studies.