The hallmark of enterohemorrhagic Escherichia coli (EHEC) and enteropathogenic E. coli (EPEC) adhesion to cultured human host cells is intimate attachment and the formation of attaching and effacing (A/E) lesions. Recently, EHEC O157:H7 was shown to induce A/E lesions on human intestinal explants. Unlike EPEC, which colonized the small intestine, EHEC adhesion was restricted to follicle-associated epithelium (FAE) of ileal Peyer's patches. This study tested the hypothesis that the bacterial adhesin intimin contributes to tissue specificity. Complementing the eae gene mutation in CVD206 (derived from EPEC strain E2348/69) with EPEC eaealpha (encoding intimin-alpha) restored the ability to colonize small intestinal mucosa like the parent strain. In contrast, complementing with EHEC eaegamma (encoding intimin-gamma) resulted in the strain adhering and inducing A/E lesion on Peyer's patches, similar to EHEC. An intimin-gamma-positive O55:H7 EPEC also targeted FAE. Thus, intimin contributes to the tissue specificity of A/E lesion-forming microbial pathogens.