Early colonic lesions in experimental Shigella infection in rhesus monkeys: revisited.

Rhesus monkeys (Macaca mulatta), given 3 x 10(8) to 5 x 10(10) Shigella flexneri 2a orally, developed signs of acute shigellosis within 24 hours. A diffuse acute colitis was well established at 48 hours. The inflammatory reaction was confined to the mucosa. The submucosa showed only edema. The shigellae were found predominantly in the columnar cells of the surface epithelium, less frequently in those of the crypt, and least frequently in the lamina propria. Shigella bacilli invaded the columnar cells from the intestinal lumen. The bacilli multiplied within epithelial cells and spread laterally to adjacent epithelial cells and penetrated the lamina propria. The bacterial invasion affected epithelial cells unevenly and resulted in the disappearance of goblet cells and pyknotic shrinkage of the surface epithelial cells. Epithelial cells had abnormal and accelerated exfoliation which resulted in multifocal epithelial defects. There was a distinct correlation between the quantity of bacilli present in tissues and the intensity of the inflammatory response. The small intestines were spared.