They are essential for the survival of bacteria, including some pathogens that cause human diseases such as septic shock. Lipopolysaccharides protect the Gram-negative bacteria against bile salts and lipophilic antibiotics, thus, contributing to conservation of bacterial structural and functional integrity.
Although lipopolysaccharide distributes on the surface of bacterial cells, its synthesis is actually initiated in the cytoplasm. Lipopolysaccharides can be divided into three parts: lipid A, core sugars and O-antigen repeats.
In most Enterobacteriacea, the lipid A structure corresponds to a bis-phosphorylated β-1-6 glucosamine disaccharide, carrying fatty acids (FA) in ester- and amide-linkages. Lipid A is known to be responsible for the toxic effects of infections with Gram-negative bacteria.
The O-antigen is a repeating oligosaccharide unit typically comprised of two to six sugars. The O-antigen is the primary structural constituent of lipopolysaccharide that differentiates bacteria.
Lipopolysaccharide contributes to the outer membrane’s integrity, it constitutes an efficient permeability barrier to antimicrobial compounds, and a protection against the complement-mediated lysis thanks to the length of its O-chains.
Lipopolysaccharides
