Effect of Haemophilus somnus on bovine endothelial cell in organ culture.

The effect of 2 strains of Haemophilus somnus on bovine endothelial cells in cultured arterial segments was investigated and compared with the effects of Escherichia coli and Salmonella typhimurium. In cultures inoculated with either strain of H somnus, there was widespread contraction and desquamation of endothelial cells, exposing large areas of subendothelial collagen. Many bacteria were adherent to endothelial cells and some were in phagosomes within cells. Endothelial changes were milder in arterial cultures inoculated with E coli or S typhimurium than in those inoculated with either strain of H somnus. Adhesion of H somnus to vascular endothelial cells followed by exposure of subendothelial collagen may initiate the thrombosis, vasculitis, and ischemic necrosis characteristic of infectious thromboembolic meningoencephalitis in cattle. Arterial cultures might be useful in assaying the virulences of different strains of H somnus, and could be used to investigate the mechanism of their action on endothelial cells.