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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.