ISOLATION AND SEROLOGIC CHARACTERIZATION OF AIDA-I, THE ADHESIN MEDIATING THE DIFFUSE ADHERENCE PHENOTYPE OF THE DIARRHEA-ASSOCIATED ESCHERICHIA-COLI STRAIN-2787 (O126-H27)

The adherence of diarrhea-associated Escherichia coli to the small-bowel mucosa is an important step in the pathogenesis of diarrheal diseases. In tissue culture systems, diarrhea-associated strains show three distinct patterns of adherence: localized adherence, diffuse adherence (DA), and the recently described aggregative adherence. To study the molecular basis of the DA phenotype, we investigated the diarrhea-associated DA strain 2787 (O126:H27), isolated from a case of infantile diarrhea. The DA phenotype is mediated by a 6.0-kb DNA fragment derived from a 100-kb plasmid harbored by the wild-type strain. This fragment codes for a 100-kDa protein which can be released from the bacterial cell into the supernatant by mild heat treatment. Recombinant DA+ strains as well as the isolated 100-kDa protein were used to engender specific antisera in rabbits. As demonstrated by Western blotting (immunoblotting), the antibodies engendered by the recombinant DA+ strain recognized a 100-kDa protein in the wild-type strain 2787 and in all recombinant strains showing DA. Immunogold electron microscopy localized the 100-kDa protein to the bacterial cell surface. Serologically related proteins of similar size were detected by Western blotting in other DA+ diarrhea-associated strains belonging to enteropathogenic E. coli serotypes. The 100-kDa protein denoted AIDA-I (adhesin involved in diffuse adherence) binds in a saturable fashion to HeLa cells. AIDA-I-specific immunoglobulin G antibodies-and, to an even greater extent, Fab fragments derived thereof-inhibited bacterial attachment to HeLa cells. This is direct evidence that the 100-kDa protein is the adhesin mediating the DA phenotype of these diarrhea-associated strains and is representative of a group of serologically related proteins in other DA+ strains.