Escherichia coli (named after Theodor Escherich, 1857-1911) is a gram-negative, rod-shaped bacterium. Like all gram-negative bacteria it has an inner and outer membrane. The latter is covered by lipopolysaccharides, LPS, which consist of an O-antigen, a core structure and a lipid A moiety. This database contains structures of the repeating units that comprise the O-antigen.