Isolation and characterization of the localized adherence factor of enteropathogenic Escherichia coli

Abstract

The binding factor of enteropathogenic Escherichia coli O111:H- responsible for localized adherence (LA) on HeLa cells was investigated. Inhibition of LA by carbohydrates and lectins showed that the reactive epitope on HeLa cells contains N-acetylgalactosamine units. Treatment of bacteria with EDTA for extraction of lipopolysaccharides eliminated these polymers as binding factors. Such treatment also caused a marked increase in adhesion suggesting steric hindrance by lipopolysaccharides of the LA factor binding capacity. Immunoblotting with rabbit antibodies showed a strong reaction with two components with approximate molecular sizes of 29 and 32 kilodaltons (kDa) present in the outer membrane preparations of bacteria. Both the absorbed rabbit immune serum and the outer membrane preparation of the bacteria inhibited bacterial adhesion by 100%. Outer membrane components were isolated from an N-acetylgalactosamine-agarose column by elution with KSCN, labeled with 125I, and immunoprecipitated with absorbed rabbit hyperimmune antiserum. The only component precipitated was the protein doublet at 29 to 32 kDa corresponding to the components detected by immunoblotting. The predominant component was always the 32-kDa polypeptide. We conclude that this component of the outer membrane is the best candidate for the LA factor in enteropathogenic E. coli.