Food safety aspects of toxins and adhesins of verotoxigenic and enterohaemorrhagic Escherichia coli (VTEC and EHEC) in farm animals

摘要

This study briefly reviews our present knowledge on toxins and adhesins, the two main virulence attributes of human-, and animal pathogenic strains of verotoxigenic E. coli (VTEC), and gives indications about the possibilities of gene transfer betweencommensal and pathogenic E. coli bacteria leading to development of new VTEC clones. At present it seems that the most widely distributed human pathogenic VTEC clones are the serotype O157:H7 and O157:NM strains most frequently originating from cattle and sheep. However, other animal species and several other types of VTEC/EHEC can be of concern and may cause serious outbreaks. These new types can be developed due to transmitibility of the toxin genes through phages and due to flexibility of the adhesin genes (on the locus of enterocyte effacement =LEE) of the chromosome. In humans, VTEC infection may lead to gastroenteritis with watery to bloody diarrhoea and in severe cases to "haemorrhagic colitis" (HC), and to haemolytic uraemic syndrome (HUS) anddeath. Transmission of VTEC from animal to man occurs mainly via contaminated food, but contaminated water and environment as well as human to human contact may also be the source of infection. The greatest concern for man are fresh meat (contaminated directly or indirectly during slaughter and/or processing), minced beef and fermented beef products, milk and milk products, fresh fruits and vegetables, herbs and spices. In Hungary the EHEC strains are of relatively less concern. So far only sporadic diseases could be detected in man, and -based on a representative survey on slaughter cattle - a low (2,5%) incidence of VTEC O157 or of other serogroups of VTEC was detected.