FIG. 8.

Representative examples of the gross pathology and histopathology of Peyer's patches and the terminal ileum of calves inoculated orally with 10¹⁰ CFU of different Salmonella serotype Typhimurium strains. (A) Severe acute fibrinopurulent necrotizing enteritis with segmental or continuous pseudomembrane formation in a calf infected with wild-type strain IR715 (similar pathological changes were observed in calves infected with the sopA mutant, the sopD mutant, or the sopE2 mutant). Bar = 1 cm. (B) Marked subacute fibrinopurulent necrotizing enteritis often confined to the Peyer's patches of the terminal ileum of a calf infected with strain ZA10 (sipA). Bar = 1 cm. (C) Normal Peyer's patches and ileum of a calf infected with strain ZA21 (sipAsopABDE). Bar = 1 cm. (D to F) Hematoxylin- and eosin-stained sections of Peyer's patches of calves infected with IR715, ZA10 (sipA), and ZA21 (sipAsopABDE), respectively. The short arrows indicate areas of lymphoid depletion; the long arrows indicate various degrees of fibrinopurulent necrotizing ileitis at the mucosal surface. Bars = 200 μm.