Relationship between lipopolysaccharide composition and virulence of Haemophilus ducreyi

The relationship between lipopolysaccharide (LPS) composition and virulence of Haemophilus ducreyi strains was investigated. Glycoses identified in LPS by gas-liquid chromatography were glucose, galactose, and their amino derivatives glucosamine and galactosamine. Fucose was found in trace amounts but mannose and rhamnose, characteristic of the O-side chain of LPS in many species, were not detected. Qualitatively, the LPS composition of the eight strains examined was similar and differences were mainly quantitative. The total glycose:KDO ratio of the LPS of virulent strains exceeded that of avirulent strains. All strains had similar fatty-acid composition but lacked lauric acid. SDS-polyacrylamide gel electrophoresis of the LPS of virulent and avirulent strains also revealed differences in their electrophoretic mobilities. The LPS profiles of avirulent strains were similar, but differed from those of virulent strains. These profiles lacked high mol. wt bands representing O-side chain repeating units. Thus, differences in the electrophoretic mobilities of the LPS of virulent and avirulent strains may reflect differences in the amount of carbohydrates associated with the core polysaccharide.