Escherichia coli-polysaccharide-protein conjugate vaccine

The present invention relates to a method of producing an E. coli vaccine and to the vaccine produced thereby. The method involves purifying lipopolysaccharide from E. coli expressing complete O-polysaccharide sidechains;isolating the O-polysaccharide region of the lipopolysaccharide molecule by hydrolysis in dilute acetic acid and purifying it essentially free of lipid A; and covalently coupling lipid A-free O-polysaccharide via at least one hydroxyl or carboxyl group of the polysaccharide to a carrier protein. Polyvalent vaccines are prepared by combining two or more monovalent vaccines for different serotypes prepared according to the present invention. The present also relates to conjugates used in the vaccines. The conjugates of the present invention are the O-polysaccharide region of an E. coli lipoplysaccharide molecule covalently coupled to a carrier protein.