Invasion of enterocytes in cultured porcine small intestinal mucosal explants by Salmonella choleraesuis.

Porcine small intestinal explants maintained in vitro were inoculated with Salmonella choleraesuis to study the characteristics of its invasion of enterocytes. The explants were fixed at selected intervals for up to 12 hours after inoculation and examined by conventional light microscopy, immunoperoxidase staining, and transmission electron microscopy. Although there was diffuse loss of villous enterocytes during the first hour of incubation, the villi were reepithelialized by the end of 2 hours of culture, and the mucosal epithelium remained intact and appeared to be viable through 12 hours of culture. Intraepithelial S choleraesuis were not detected before 6 hours after inoculation, but after 12 hours of incubation, bacteria were numerous within enterocytes. Ultrastructurally, penetration of the brush border by S choleraesuis resulted in focal loss of microvilli. Bacteria were endocytosed into membrane-bound vacuoles where most remained, but a few were free within the cytoplasm of enterocytes. Invasion of the explants closely resembled that described for live animal and cell culture models of Salmonella spp invasion.