Interaction of a Δtir derivative of EHEC O157:H7 strain TUV 93-0 with the bovine intestinal mucosa. Only a few O157-positive bacteria were observed close to the ileal epithelium following the immunostaining of a formalin-fixed, paraffin-embedded section, whereas no O157-positive bacteria were found in the terminal colon and terminal rectum. Hoechst 33342 (blue, false color), nuclei and bacteria; tetramethyl rhodamine isothiocyanate (TRITC) (red, false color), O157-positive bacteria. Bar = 10 μm.