FIG. 3.

Representative transmission electron micrographs (at the same magnification) from jejunum (A, C, and F) and proximal colon (B, D, E, and G) of control (A and B), infected untreated (C to E), or EGF-treated (F and G) rabbits 7 days after infection with E. coli RDEC-1 or sham inoculation. In tissues from infected untreated animals, ultrastructural observations revealed colonization by gram-negative bacteria (∗), localized deletion of individual microvilli, formation of apical pseudopods devoid of microvilli on enterocytes (arrow), and generalized shortening of microvilli along the entire epithelial surface in the jejunum (C). Bacteria did not invade the epithelium and did not compromise the integrity of junctional complexes (arrowheads). In specimens from the EGF-treated group, gram-negative bacteria were seen less frequently, and disruptions to the epithelial brush border were inhibited. In the jejunum of EGF-treated infected rabbits (F), microvillous length was restored to that observed in tissues from controls (A). Bar = 1 μm.