Polysaccharide

Polysaccharide

	Polysaccharide - The polysaccharide component of Salmonella LPS has been extensively described. The polysaccharide chain consists of three components, the inner core, the outer core and the a-antigen side chain. The rough strains (R forms) of gram negative bacteria completely lack the O-antigen side chains. Their LPSs have only inner core and outer core chains. The inner core region is believed to be the same in all strains of Salmonella, but differs in other genera. It consists of two regions, the KDO region and the diheptose region.
The KDO region consists of three units of ketodeoxyoctonate (KDO), an 8-carbon α-keto sugar acid. The diheptose region contains two units of a 7-carbon heptose sugar called L-glycero-D-mannoheptose (Hep). KDO and Hep are, unique to bacterial cell walls. The smooth strains of Salmonella have intact O-antigen side chains, which may extend to as much as 30 Dm from the wall surface. These chains have antigenic properties. In a particular LPS every O-antigen side chain contains the same repeating sequence. There may be up to 40 repeating units in a chain, which vary in length even in the same organism.
The repeating sequence may be a linear trisaccharide or a branched tetra-or pentasaccharide. Specific antibodies can be prepared against the polysaccharides, and about a thousand different ‘serotyps' of Salmonella are known. These have been classified into 17 main groups. In certain strains of E. coli the O-antigen chain contains colitose (col).

Home | Site map | Submit Article | Resources | Search