Escherichia coli O-serotype O-antigen polysaccharide (None standard; occasionally "E. coli O-antigen" or, for specific serotypes, "E. coli O[serotype] O-antigen" (e.g., "E. coli O125 O-antigen"))

The *Escherichia coli* O-serotype O-antigen polysaccharide is the distal, repeating polysaccharide chain component of lipopolysaccharide (LPS) found on the outer membrane of Gram-negative *E. coli* bacteria[2][3]. Each O-serotype is defined by a unique O-antigen structure, typically composed of 10–25 repeating oligosaccharide units that vary in sugar composition and linkage. The O-antigen is highly immunogenic, forming the molecular basis for O-serogroup classification, and is exposed on the bacterial surface, where it mediates immune evasion, interacts with host defenses, and serves as a receptor for bacteriophages. These O-polysaccharides are primary targets for vaccine design, diagnostic tests, and phage therapy against *E. coli* infections. The high chemical diversity among O-antigens underlies the pathogenic variability and adaptability of *E. coli* strains[1][2][3].

Other names

Escherichia coli O-antigenE. coli O-polysaccharideE. coli serogroup O-antigenLipopolysaccharide O-antigen (or LPS O-antigen)O-specific polysaccharide

Vaccines/antibodies induce or mediate immune recognition and clearance of bacteria expressing the targeted O-antigen serotype. Phages adsorb to the O-antigen structure as a receptor; subsequent steps lead to bacterial lysis.