Purified rat intestinal mucin was used as a model mucin to study the binding of Escherichia coli serotype O157:H7, a human pathogen associated with outbreaks of hemorrhagic colitis and hemolytic uremic syndrome. Of six O157:H7 strains, only one strain (designated CL-49) bound to rat (and other) intestinal mucins by a specific and saturable process. Binding was observed only after the bacteria were serially passaged to promote the expression of type 1 pili (fimbriae). Several other type 1-piliated E. coli strains, however, did not bind to mucin. Binding of E. coli CL-49 was inhibited by D-mannose and short oligomannosyl derivatives, particularly Man-alpha-1,3-Man, Man-alpha-1,2-Man, and Man-alpha-1,3-Man-beta-1,4-N-acetylglucosamine. Other inhibitors of binding included p-nitrophenol (10(-4) M), heating at 60 degrees C (to remove pili), an antibody to type 1 pili, and purified type 1 pili of E. coli CL-49 used as hapten inhibitors. A comparison of the hydrophobicity of piliated E. coli CL-49 with other type 1-piliated E. coli strains indicated that the former strain was much more hydrophobic than the others. These findings indicate that highly purified intestinal mucins possess specific mannosyl receptor sites for bacterial type 1 pili on E. coli CL-49, but that strong hydrophobic interactions between the mucin and the pili stabilize the mannose-dependent binding process. We speculate that the mucin receptors for type 1 pili reside in oligosaccharides of the 118-kilodalton "link" glycopeptide, since this is the only mucin component known to contain mannose.