Infections caused by vero/shiga-toxin-producing Escherichia coli in domestic animals

A review of Vero-toxin (VT) and "Shiga-like" toxin (SLT) producing Escheric hia coli (VTEC and SLTEC respectively) induced infections in animals is giv en: from the nomenclature to molecular pathogenesis and to special characte ristics of toxin groups. As the toxins of these groups are generally charac terized by the same or similar structure and pathomechanisms as the toxin o f Shigella dysenteriae (composed of one A and five B subunits), it is sugge sted that in the Hungarian literature the toxins should be labelled as Stx and the toxin producing E. coli bacteria be designated as STEC. These toxins produce systematic and enteric disease in man (Stx1, Stx2)! pr actically only enteric disease (or mostly carrier state) in bovine and in o ther ruminants (Stx1, Stx2), and only systemic disease in pigs (Stx2v). The pathomechanism of these toxins is characterized by the receptor mediate d endocytosis (Fig.1), followed by fusion with lysosmes and release of the enzymatically active fragment Al, leading to inhibition of protein synthesi s and cell death. Most of the STEC bacteria of ruminants and men produce the characteristic " attachment effacement" (AE) lesion accompanied by microvillus degeneration and bacterial adhesion (Fig.2), and formation of cups and pedestals of the intestinal epithelial cell membranes at the site of attachment. The mediator of attachement is a bacterial outer membrane protein (intimin) . In contrast, no intestinal cytoskeletal rearrangement or lesion is induce d by porcine STEC (Fig.3): bacteria of the oedema disease producing E. coli adhere to the intact microvilli of the small intestinal epithelial cells. This adhesion is similar to that of enterotoxic E. coli (ETEC) and mediated by morphologically and antigenically related fimbriae (Fig.4) called F18ab and F18ac respectively. Members of this large group of STEC bacteria (primarily E. coli strains of serotype O157:H7) are able to induce zoonoses (infections from animals to m en). Porcine oedema inducing STEC strain provide an exception as there is no evi dence for such strains to colonize man.