O-antigen of Escherichia coli serotype O1A

The O-antigen of *Escherichia coli* serotype O1A is a distinctive surface polysaccharide consisting of repeating oligosaccharide units that make up the outermost region of LPS. Its molecular structure is characterized as a linear pentasaccharide repeat, conserved in invasive bloodstream isolates from genotypic subgroups ST95, ST38, and ST59. This antigen is critical for defining E. coli serogroup identity, mediating immune evasion, and is a target for vaccine development—specifically in conjugated forms that elicit protective antibody responses in animal models. Natural variation in the O-antigen structure underlies serogroup diversity and impacts pathogenicity and host interaction. The O1A subtype, in particular, is associated with virulent strains causing neonatal sepsis and bloodstream infections, and is generally linked to strains with the K1 capsule enhancing invasiveness[1][2][3]. The O-antigen is not directly targeted by antibiotics, but its characterization informs vaccine antigens and monoclonal antibody development for preventing or treating serious E. coli infections.

Other names

O1A polysaccharideLPS O1A antigenEscherichia coli O1A O-antigen

Vaccine-induced antibody response (antibody opsonization and complement-mediated killing); Blocking LPS-mediated immune evasion