BLonger chain antigenic O polysaccharide chains for use as a hapten in conjugate vaccines can be produced in a controlled manner using recombinant Gram negative bacteria that overexpress native or heterologous genes of the family for example. Bacteria expressing a chosen wzz gene have modified O polysaccharide chain lengths allowing the bacteria to produce lipopolysaccharides having the longer O polysaccharides. The LPS produced by the bacteria can be hydrolyzed to form core O polysaccharide molecules that can be conjugated to a carrier molecule for example flagellin to produce a vaccine. The invention also provides recombinant bacteria producing the longer chain O polysaccharides the polysaccharide molecules themselves conjugated vaccines comprising the O polysaccharides pharmaceutical compositions and kits.
