Biological and immunological characterization of pili of Escherichia coli serotypes O1, O2, and O78 pathogenic to poultry

Pili of Escherichia coli serotypes O1, O2, and O78 pathogenic to poultry were isolated and purified by sucrose-density-gradient centrifugation. Each serotype expressed only one type of pilus. The pili of the three serotypes had similar densities and were morphologically similar by electron microscopy. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis, however, showed that they were slightly different in subunit molecular mass. Slide agglutination, immunodiffusion, and immunoblot tests were used to test for antigenic relationships between these pili and reference pili. Pili of serotype O78 were type 1, but pili of serotypes O1 and O2 were not, as once believed. However, pili of serotype O2 reacted positively with anti-type 1 serum in immunoblot assay, suggesting the presence of some common antigenic epitopes among these pili.