Bacteria, gram-negative, complex polysaccharides

As shown in Figure 9.24, the outer membrane of Gram-negative bacteria is coated with a highly complex lipopolysaccharide, which consists of a lipid group (anchored in the outer membrane) joined to a polysaccharide made up of long chains with many different and characteristic repeating structures... 

Figure 7.7 Structure of a generalized LPS molecule. LPS constitutes the major structural component of the outer membrane of Gram-negative bacteria. Although LPSs of different Gram-negative organisms differ in their chemical structure, each consists of a complex polysaccharide component, linked to a lipid component. Refer to text for specific details...

Gram-negative bacteria have a more complex cell surface. The peptidoglycan layer is also the outer layer with respect to the cytoplasmic membrane. However, besides this, they have another outer polysaccharide membrane. This outer membrane is built out of lipopolysac-charides and lipoproteins, and can be a serious barrier for permeating hydrophilic molecules. 

Gram-negative bacteria have a cell envelope containing two membranes, with the outer membrane having lipopolysaccharide in its outer leaflet. Lipopolysaccharide is complex and consists of four parts. On the outside is the O-antigen which is a polysaccharide of variable structure. This is attached to a core polysaccharide which is in two parts, an outer core and a backbone. The backbone is connected to a glycolipid, called lipid A, through a... 

Gram-negative bacteria contain lipopolysac-charide in the outer membrane of their cell envelope. The lipopolysaccharide is a complex polymer with four parts. On the outside is a polysaccharide of very variable structure which is then attached to a core polysaccharide which itself is divided into an outer core and a backbone. The outer cores are variable in composition but the link which connects the backbone to lipid A is usually composed of 3-deoxy-D-manno-octulosonic acid (KDO). The presence of KDO (Fig 3.3) is often used as a marker for lipopolysaccharide or outer membrane. 

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. 

Severe nutritional deficiencies, X-irradiation, the administration of antifolic (see Fig. 4-48) or bactericidal agents allow some bacteria of the intestinal lumen to pass through the mucosa and enter the bloodstream to cause septicemia. Furthermore, the endotoxins normally present in the intestinal lumen enter the bloodstream under certain pathological conditions and transform reversible shock into irreversible shock. All gram-negative bacteria produce endotoxins—large molecules with a molecular weight of 1,000,000 formed of a complex of proteins, lipids, and polysaccharides. 

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