High-molecular-weight components in lipopolysaccharides of Salmonella typhimurium, Salmonella minnesota, and Escherichia coli

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Abstract
Lipopolysaccharide from smooth strains of S. typhimurium, S. minnesota and E. coli O111:B4, O55:B5 and O127:B8 was fractionated by gel filtration chromatography. All lipopolysaccharide samples separated into 3 major populations. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the fractions from S. typhimurium and S. minnesota indicated that the 3 peaks were made up of molecules with average O-antigen lengths of .gtoreq. 70 repeat units, 30 and 20 repeats units in the samples from S. typhimurium and S. minnesota, respectively, and 1 repeat unit. In contrast to the Salmonella samples, peak 1 from the E. coli samples was not detected on polyacrylamide gels and lacked detectable phosphate. This high-MW material had a sugar composition similar to that of O-antigen and was tentatively identified as capsular polysaccharide. Peaks 2 and 3 of the E. coli samples were analogous to those of the Salmonella isolates, containing lipopolysaccharide molecules with averages of 18 and 1 O-antigen repeat units, respectively. These lipopolysaccharide molecules did not completely dissociate during electrophoresis, and multimers were detected as distinct, anomalous, slow-migrating bands. Increasing the concentration of sodium dodecyl sulfate in the gels resulted in the dissociation of these multimers.