FIG. 1.

(A and C) Horseradish peroxidase-stained sections of colon from a neonatal pig necropsied 49 h after inoculation with STEC O157:H7 strain 86-24 (A) or from a pig necropsied 41 h after inoculation with strain B2F1 (C), showing typical immunostained colonies of O157:H7⁺ A/E bacteria (A) and adherent O91⁺ bacteria (C) on the mucosal surface. (B and D) Electron micrographs showing intimately attached bacteria and effaced microvilli in the cecum from a pig necropsied 18 h after inoculation with strain 86-24 (B) (magnification, approximately ×6,000) and adherent bacteria and intact villi on the surface of absorptive epithelial cells in the colon from a pig necropsied 43 h after inoculation with strain B2F1 (D) (magnification, approximately ×3,500).