Bacteriostatic effect of serum: role of antibody to lipopolysaccharide

Abstract

Antibody [Ab] and transferrin acting together exert a bacteriostatic effect on certain pathogenic Escherichia coli. This effect may be due to the ability of the Ab to interfere with the release of the Fe chelator, enterochelin, from the bacterial cell. Enterochelin is essential for the transport of Fe from transferrin to the bacterial cell. The nature of the bacterial antigen [Ag] against which the Ab is directed was determined by adsorption experiments. Absorption of serum with heat-killed cells of E. coli O111 or with Boivin Ag abolished the bacteriostatic effect. A monosaccharide, colitose (3,6-dideoxy-L-galactose), was isolated after acetic acid hydrolysis of the Boivin Ag. 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 whole serum and mixtures of Ab and Fe-binding proteins. When administered i.p., it reduced the resistance of mice to subsequent infection with E. coli O111. This ability of colitose to interfere with antibacterial mechanisms agrees with published immunochemical studies.