Enterohemorrhagic E coli

<p>All strains of EHEC contain lysogenic bacteriophage encoding one or more Shiga toxins that are responsible for the vascular damage (hemorrhagic colitis) and for the systemic effects of infection, such as hemolytic-uremic syndrome. These toxins from EHEC belong to a larger Shiga toxin family, which includes the closely related Shiga toxin produced by Shigella dysenteriae type 1 . There are two related types of Shiga toxins in EHEC defined serologically (Shiga toxin 1 and 2), as well as a number of subtypes of Shiga toxin 2.

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Shiga toxins enter the systemic circulation and are bound to polymorphonuclear leukocytes . In the systemic circulation, Shiga toxins target endothelial cells, causing vascular damage, bloody diarrhea, and, in some patients, a prothrombotic state that precedes the hemolytic uremic syndrome . Expression of toxin receptors on endothelial cells is upregulated by tumor necrosis factor-alpha (TNFa) and interleukin (IL)-1b; these cytokines are, in turn, released by the interaction of Shiga toxins with macrophages and monocytes .</p>