Studies on the pathogenesis of Salmonella heidelberg infection in weanling pigs. 
Experiments were conducted to define the pathogenic potential of Salmonella heidelberg in weanling pigs.  Oral inoculation with S heidelberg resulted in severe catarrhal enterocolitis with accumulation of large amounts of fluid in the small intestine and colon.  Salmonella heidelberg was demonstrated, with fluorescence microscopy and bacteriologic cultural techniques, to colonize the ileum, to invade ileal mucosal enterocytes, and to reach mesenteric lymph nodes and extraintestinal tissues by 8 hours.  In 5 pigs, intestinal loops were surgically prepared and inoculated with S heidelberg (to determine its invasiveness).  Microscopically, there were atrophy of villi, erosion of enterocytes, and neutrophilic infiltration in the lamina propria.  Ultrastructurally, intracellular bacteria were demonstrated in villous and cryptal enterocytes, as well as in macrophages of the lamina propria.  Bacteria were morphologically intact, occurred free and membrane-bound and caused no detectable cytotoxic effect to the cell.