Molecular Structure, Biosynthesis, and Pathogenic Roles of Lipopolysaccharides

Like the cell envelopes of other gram-negative bacteria, that of contains lipopolysaccharides (LPSs), which are a family of toxic phosphorylated glycolipids that are also termed endotoxins (57). In general, LPSs are essential for the physical integrity and functioning of the bacterial outer membrane (34) and, as the main surface antigens (O-antigens) of gram-negative bacteria, play an important role in the interaction of these bacteria with their environment and with higher organisms (34, 57, 93). LPSs are potent immunomodulating and immunostimulating compounds, due principally to their lipid component, lipid A (93, 94). This family of compounds also harbors binding sites for antibodies and nonimmunoglubulin serum factors (34, 93). Generally, LPSs possess a broad spectrum of endotoxic properties, e.g., pyrogenicity and lethal toxicity, which contribute to the pathogenic potential of gram-negative bacteria (57, 93, 94). Moreover, variation in the structure of the saccharide component of LPS may prevent efficient complement activation and phagocytosis, thereby contributing to the virulence of bacterial strains (44, 93). Despite the established importance of LPSs in bacterial pathogenesis, those of have received more limited attention compared with LPSs of other bacterial pathogens. Evidence has accumulated that, although possessing properties similar to those of other gram-negative bacteria, the LPSs of also possess unique biological properties. In this chapter the attributes and structure of LPSs, especially the relationship between molecular structure and pathogenesis, are reviewed.