Lipopolysaccharide alteration mediated by the virulence plasmid of Salmonella.

Lipopolysaccharide (LPS) of Salmonella dublin, S. enteritidis, S. typhimurium, S. choleraesuis and their derivative strains was analysed to investigate the correlation between LPS and virulence plasmid of Salmonella. All wild-type strains had smooth type LPS, i.e. LPS with long O-specific polysaccharide. The virulence plasmid-cured strain of S. dublin, C524, exhibited a shorter O-specific chain than its parent strain, 5240. No distinct ladder bands were observed at the high molecular weight region on the SDS-PAGE gel for C524 LPS. By chemical analysis the number of O-repeating unit of C524 LPS was shown to be approximately one. The chain length of O-specific polysaccharide was restored by reintroduction of the virulence plasmid. The alteration of LPS by curing and reintroduction of the virulence plasmid was not observed when other wild-type strains of S. dublin were used. In the case of S. enteritidis, S. typhimurium, and S. choleraesuis, alteration of neither chemical composition nor electrophoretical profile of LPS was detected by curing and reintroduction of the virulence plasmids. Those results suggest that certain factor for regulation of the chain length of O-specific polysaccharide is encoded on the virulence plasmid of S. dublin.