A comparison of the morphologic effects of Serpulina hyodysenteriae or itsbeta-hemolysin on the murine cecal mucosa

Studies were carried out to compare the early morphologic changes in the ce cal mucosa of mice either infected with Serpulina hyodysenteriae or exposed to the P-hemolysin of S. hyodysenteriae. Sixty-five 12-24-week-old C3H/HeO uJ mice were infected with S. hyodysenteriae by gastric intubation. Two mic e were necropsied every hour for 30 hours following infection. S. hyodysent eriae was isolated from the cecal contents of each mouse at all time points . Macroscopic lesions were first apparent at 14 hours postinfection (PI), a nd light microscopic lesions were first apparent at 10 hours PI, earlier th an 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 thr ough epithelial cells to the lamina propria, where capillaries exhibited ch anges indicative of increased permeability. In another experiment, solution s containing between 2,500 and 25,000 hemolytic units of purified S. hyodys enteriae hemolysin were placed within the lumen of surgically closed murine ceca (n = 10); ceca were collected for examination 3 hours following treat ment. 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 epith elial cells internalized moderate numbers of bacteria. The hemolysin of S. hyodysenteriae induces some of the same early ultrastructural changes in th e cecal epithelium of mice as occur following infection with S. hyodysenter iae. Based on the observed bacterial translocation, luminal bacteria also a ppear to play a unique role in lesion development in this model.