The abbreviation STEC refers to Shiga toxin-producing Escherichia coli serotypes. STEC includes subgroups of E. coli with many different characteristics and virulence factors. One of these subgroups is the EHEC (enterohemorrhagic) pathotype, which are the agents of haemorrhagic diarrhoea in humans. In addition to undercooked minced beef dishes (hamburgers), chopped meat products, unpasteurised milk, lettuce, cantaloupes, apple juice, and vegetables have all been reported as vehicles for STEC transmission. Outside the mammalian intestinal tract, intestinal bacteria are threatened by predatory protozoa. STEC strains carrying stx genes have developed a defence strategy based on the production of Shiga toxin able to kill eukaryotic cells. STEC pathogenesis in humans involves the initial adhesion of bacteria to the intestinal epithelium in the ileum and, later, colonisation of the colon with the production of the Shiga toxin. The barrier function of the epithelium and ion transport are disrupted, causing diarrhoea. A pathogenicity island called LEE (locus of enterocyte effacement) is a crucial genome segment for EHEC pathogenesis.
