Salmonella, complex polysaccharides

In Salmonella spp. the core region of lipopolysaccharide has quite a complex structure and forms a well-defined domain this is not so in some other genera, where the core is either considerably simpler, or effectively absent, so that the polysaccharide antigen is attached more or less directly to lipid A. 

The cell wall of bacteria has a complex structure. The matrix is formed by the peptidoglycan murein which is a single macromolecule. It is built from polysaccharide chains interlinked by peptide bridges (Fig. 337). This network is covered by a layer of proteins. Additionally the cell wall of gram negative bacteria, e.g., Escherichia coli Salmonella and Shigella species contains large quantities of lipids. 

The formation of lipid-linked sugars in vitro by Bacillus stearothermophilus. Salmonella typhimurium, and Shigella jlexneri requires an unsaturated a-isoprenyl residue in a polyprenyl phosphate, in contrast to th- t in rat-liver microsomes which requires a saturated a-isoprenyl residue. o-Glucopyranosyl polyprenyl phosphate was formed on incubation of UDP-D-[ C]glucose with particulate preparations from B. stearothermophilus, and it may serve as a D-glucosyl donor in the synthesis of an extracellular polysaccharide. The properties of the membrane-associated sialyltransferase complexes of Escherichia coli have been examined. These complexes catalyse the incorporation of iV-acetylneuraminic... 

The Salmonella are examples of such pathogens. There are hundreds of Salmonella species and strains that produce immunologically distinct 0-antigen polysaccharides. This apparent complexity, results from relatively small variations of a single basic structure. 

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