CHARACTERIZATION OF 20K FIMBRIA, A NEW ADHESIN OF SEPTICEMIC AND DIARRHEA-ASSOCIATED ESCHERICHIA-COLI STRAINS, THAT BELONGS TO A FAMILY OF ADHESINS WITH N-ACETYL-D-GLUCOSAMINE RECOGNITION

Bovine septicemic Escherichia coli 31A agglutinates bovine, rabbit, an d human erythrocytes and adheres in vitro to the brush border of bovin e or ovine intestinal epithelial cells and to the human colon carcinom a Caco-2 cell line. The adhesion and hemagglutination of E. coli 31A a re mediated by a chromosome-encoded fimbrial adhesin serologically dis tinct from known fimbrial adhesins found in enterotoxigenic and septic emic bovine E. coli strains. By electron microscopy studies the fimbri ae designated 20K were observed as fine flexible filaments (diameter, 3 um) and the purified major fimbrial subunit appeared with an apparen t molecular mass of 20,000 Da. Western blot (immunoblot) analysis, N-t erminal sequence alignment, and amino acid composition revealed a high homology with the N-acetyl-D-glucosamine-specific G fimbria of human uropathogenic E. coli and with fimbriae belonging to the F17 family pr oduced by bovine enterotoxigenic and invasive E. coli strains. Immunol ogical study revealed that 20K fimbria was closely related to G fimbri a and represents a serological variant of F17 fimbria. Hemagglutinatio n and adhesion inhibition assays demonstrated that 20K, G, and F17 fim briae bind to an N-acetyl-D-glucosamine-containing receptor, but each probably binds to different oligosaccharide sequences or different rec eptors on host tissues, 20K fimbriae were produced by a limited group of clonally related strains with the unusual m-inositol-positive pheno type and appeared highly associated with the plasmid-encoded CS31A sur face antigen. It was expected that 20K- and CS31A-positive E. coli str ains with the m-inositol-positive phenotype could represent a new exam ple of association between bacterial clones and a plasmid-mediated vir ulence factor. An examination of natural occurrence of 20K fimbriae am ong a large collection of human and animal pathogenic E. coli showed t hat 20K fimbria is the prominent adhesin among bovine septicemic E. co li isolated from European countries.