title: Form variation in Escherichia coli K1: determined by O-acetylation of the capsular polysaccharide.
abstract: The chemical basis for the alternating antigenic change called form variation noted for the Escherichia coli K1-capsular polysaccharide has been shown by 13C nuclear magnetic resonance to be a result of random O-acetylation of C7 and C9 carbons of the alpha-2-8-linked sialic acid homopolymer. A serologic method (antiserum agar) was developed to identify and isolate the form variants. The O-acetyl positive and O-acetyl negative K1 polysaccharides had unique biochemical and immunologic properties. The O-acetyl-positive variants resisted neuraminidase hydrolysis in contrast to the susceptibility of the O-acetyl negative variant to this enzyme. In addition, O-acetylation altered the antigenicity of the O-acetyl polysaccharides. When injected as whole organisms, O-acetyl positive organisms produced anti-K1 -antibodies in rabbits specific for this polysaccharide variant. O-acetyl negative organisms were comparatively less immunogenic; however, antibodies induced by these organisms reacted with both K1 polysaccharide variants. Burros, injected with either variant, produced antibodies reactive with both K1 polysaccharides.
mesh_terms: D000107:Acetylation; D000907:Antibodies, Bacterial; D000917:Antibody Formation; D000942:Antigens, Bacterial / Q000032:analysis*; D004926:Escherichia coli / Q000276:immunology*; D009682:Magnetic Resonance Spectroscopy; D009439:Neuraminidase / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000276:immunology*; D012703:Serotyping; D012794:Sialic Acids
chemical_list: D000907:Antibodies, Bacterial; D000942:Antigens, Bacterial; D011135:Polysaccharides, Bacterial; D012794:Sialic Acids; D009439:Neuraminidase