FIG. 6.

Effects of zinc on EPEC-induced fluid secretion, intestinal adherence, EPEC bacterial numbers, and histologic damage in the rabbit ileal loop model of infection. Ten-centimeter ileal loops were infected with 10⁹ CFU of EPEC E2348/69, and intestinal loops and loop fluid samples were recovered 18 to 20 h later. (A and B) Gross-view photographs of the EPEC-infected loops in the absence (A) or presence (B) of 1 mM zinc acetate, added once at the time of infection. Loop L5 in each rabbit was the uninfected control. (C) Volume-to-length ratios of fluid accumulation in intestinal loops. The asterisk indicates a significant decrease compared to the value for the no-zinc condition. (D) Gross-view photograph of ileal loops infected with 10⁸ CFU per loop of rabbit EPEC strain E22, showing that the protective effects of zinc were confined to the loops actually treated with zinc, with no cross-protection of neighboring untreated loops. (E to H) Effect of zinc on histological damage induced by human EPEC E2348/69 infection; ileal tissues were fixed, stained with hematoxylin and eosin stain, and photographed at a magnification of ×100. (E) Uninfected control ileum, showing long slender villi; (F) ileum infected with EPEC E2348/69 for 20 h, showing EPEC adherence primarily at the villus tips (dense blue staining, indicated by arrowheads), with villus blunting and crypt hyperplasia; (G) ileum infected with E2348/69 plus 0.1 mM zinc acetate, showing less villus blunting. EPEC bacteria are visible in the intestinal lumen (top of photograph), but fewer are adhering to the villi; (H) ileum infected with E2348/69 plus 1 mM zinc acetate, showing normal villus height, normal crypt depth, and no visible adherent EPEC.