Chemical Structure, Conjugation, and Cross-Reactivity ofBacillus pumilusSh18 Cell Wall Polysaccharide

Bacillus pumilusstrain Sh18 cell wall polysaccharide (CWP), cross-reactive with the capsular polysaccharide ofHaemophilus influenzaetype b, was purified and its chemical structure was elucidated using fast atom bombardment mass spectrometry, nuclear magnetic resonance techniques, and sugar-specific degradation procedures. Two major structures, 1,5-poly(ribitol phosphate) and 1,3-poly(glycerol phosphate), with the latter partially substituted by 2-acetamido-2-deoxy-α-galactopyranose (13%) and 2-acetamido-2-deoxy-α-glucopyranose (6%) on positionO-2, were found. A minor component was established to be a polymer of →3-O-(2-acetamido-2-deoxy-β-glucopyranosyl)-1→4-ribitol-1-OPO3→. The ratios of the three components were 56, 34, and 10 mol%, respectively. The Sh18 CWP was covalently bound to carrier proteins, and the immunogenicity of the resulting conjugates was evaluated in mice. Two methods of conjugation were compared: (i) binding of 1-cyano-4-dimethylaminopyridinium tetrafluoroborate-activated hydroxyl groups of the CWP to adipic acid dihydrazide (ADH)-derivatized protein, and (ii) binding of the carbodiimide-activated terminal phosphate group of the CWP to ADH-derivatized protein. The conjugate-induced antibodies reacted in an enzyme-linked immunosorbent assay with the homologous polysaccharide and with a number of other bacterial polysaccharides containing ribitol and glycerol phosphates, includingH. influenzaetypes a and b and strains ofStaphylococcus aureusandStaphylococcus epidermidis.