Escherichia coli O-antigen (E. coli O-antigen)

The **Escherichia coli O-antigen** is the highly variable polysaccharide component of the lipopolysaccharide (LPS) on the outer membrane of E. coli. It consists of repeating oligosaccharide units (commonly 2–7 sugar residues per repeat), covalently linked to the core oligosaccharide and lipid A. The structure and sequence of O-antigen repeats differ between E. coli serotypes and underpin the O serogrouping system used in epidemiology and diagnostics. O-antigens play a significant role in immune evasion, virulence, and survival in the host by masking the bacterium from the immune system and environmental threats. Their biosynthesis is determined by the chromosomal O-antigen gene clusters, which also explain the extensive diversity among strains. While not a single defined receptor or enzyme, the O-antigen is a critical epitope for serological detection and a focus for vaccine development against specific pathogenic E. coli strains.

Other names

O-specific polysaccharideO-polysaccharideO antigenO side chain of LPS (lipopolysaccharide)

For vaccines/antibodies: Induce immune response by generation of anti-O-antigen antibodies that opsonize bacteria or facilitate complement-mediated killing For antibiotics: Disrupt bacterial membrane integrity (polymyxins), but these target the entire LPS, not just the O-antigen portion