Disclosed are EspF.sub.U (EspF-like polypeptide encoded by a gene of the cryptic prophage CP-933U of enterohemorrhagic E. coli) polypeptides, fragments thereof, nucleic acids that encode EspF.sub.U polypeptides, or fragments thereof, and cells including the polypeptides, fragments, and/or nucleic acids. Also disclosed are model systems, kits, and methods for screening that use, for example, EspF.sub.U polypeptides and nucleic acids. Also included are pharmaceutical and diagnostic compositions and methods of diagnosis and treatment of EHEC infections.