A Comparison of the Morphologic Effects of Serpulina hyodysenteriae or its Beta-hemolysin on the Murine Cecal Mucosa

Studies were carried out to compare the early morphologic changes in the cecal mucosa of mice either infected with Serpulina hyodysenteriae or exposed to the β-hemolysin of S. hyodysenteriae. Sixty-five 12–24-week-old C3H/HeOuJ mice were infected with S. hyodysenteriae by gastric intubation. Two mice were necropsied every hour for 30 hours following infection. S. hyodysenteriae was isolated from the cecal contents of each mouse at all time points. Macroscopic lesions were first apparent at 14 hours postinfection (PI), and light microscopic lesions were first apparent at 10 hours PI, earlier than has been previously reported. Ultrastructural changes, first evident at 6 hours PI, included disarray and loss of microvilli and terminal web, with dilatation of intercellular spaces. Luminal bacteria were translocated through epithelial cells to the lamina propria, where capillaries exhibited changes indicative of increased permeability. In another experiment, solutions containing between 2,500 and 25,000 hemolytic units of purified S. hyodysenteriae hemolysin were placed within the lumen of surgically closed murine ceca (n = 10); ceca were collected for examination 3 hours following treatment. Ultrastructural changes consisted of loss of microvilli and terminal web and marked vacuolation and exfoliation of epithelial cells. Significant numbers of necrotic and apoptotic epithelial cells were present, and epithelial cells internalized moderate numbers of bacteria. The hemolysin of S. hyodysenteriae induces some of the same early ultrastructural changes in the cecal epithelium of mice as occur following infection with S. hyodysenteriae. Based on the observed bacterial translocation, luminal bacteria also appear to play a unique role in lesion development in this model.