Definitions of O Antigens

  1. The lipopolysaccharide- protein somatic antigens, usually from gram- negative bacteria, important in the serological classification of enteric bacilli. The O- specific chains determine the specificity of the O antigens of a given serotype. O antigens are the immunodominant part of the lipopolysaccharide molecule in the intact bacterial cell. ( From Singleton & Sainsbury, Dictionary of Microbiology and Molecular Biology, 2d ed)