Introduction

Enteropathogenic E. coli (EPEC) and enterohemorrhagic E.coli O157:H7 (EHEC) are bacteria which colonize the intestinal epithelia postijestion.  Symptoms indicating their residence include cramps, diarrhea, and in some cases progression to hemorrhagic colitis and hemolytic uremic syndrome.  These pathogens require the formation of attaching and effacing lesions on the surface of the host intestinal epithelia.  Two critical proteins for this attachment, intimin and the translocated intimin receptor (Tir), are encoded on the locus of enterocyte effacement (LEE) pathogenicity island.  Intimin  is an outer membrane protein which is required for adhesion, cytoskeletal reorganization, and complete virulence in adult hosts.  Intimin binds to epithelial cells via the translocated intimin receptor present on the cell surface. Tir is actually translocated from the bacteria into the host membrane.  Although EPEC and EHEC both translocate Tir to the host, subsequent modifications differ in the strains.  With respect to EPEC, Tir is phosphorylated.  In both EPEC and EHEC, the actin is rearranged beneath this binding site to form elongated cup-like pedestal formations, providing an intimate adherence site between the bacteria and the host cell.

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