FIG. 6.

Interaction of wild-type C. rodentium strain ICC180 and its ΔnleH mutant with the colonic epithelium in vivo. (A) At day 9 postchallenge, typical foci of intimately adherent bacteria (arrows) were observed on H&E-stained sections, accompanied by a highly disorganized epithelium. IFA staining revealed these bacteria to be of the O152 serotype (arrowheads), corresponding to C. rodentium serotype. These foci of intimately adherent bacteria were confirmed to be A/E lesions by SEM. Neither O152-positive bacteria nor A/E lesions were observed on sections or samples derived from uninfected mice. (B) No adherent bacteria were observed in the colons of mice infected with ICC180 and the ICC180 ΔnleH mutant at day 14 postchallenge, although crypt hyperplasia was still present. For the IFA panel: Hoechst 33342 (blue, false color), DNA; tetramethyl rhodamine isothiocyanate (intense blue, false color), O152-positive bacteria. Representative micrographs are shown. Bar, 20 μm (H&E and IFA) or 100 μm (B).