Zoonotic infections infections in livestock and the risk to public health - Poster Abstract

Genotyping and phenotypic profiling of bovine and human Escherichia coli O157 isolates

A McNally et al

Cattle have been implicated as important reservoirs of enterohaemorrhagic Escherichia coli (EHEC), and in particular the human pathogen E.coli O157, which is carried asymptomatically in cattle with the possible exception of neonatal calves. However certain serotypes of EHEC, particularly E.coli O26, have been associated with disease in cattle, including presence of attaching and effacing (A/E) lesions characteristic of EHEC infections.

A/E lesions are caused by the production of proteins encoded for by the Locus of Enterocyte Effacement, or LEE. As well as these virulence associated genes, EHEC also encode genes for a range of secreted proteins (Esp's), including the shiga-like toxins Stx1 and Stx2 (and variants), an enterohaemolysin (ehx), a serine protease (espP), a large toxin with homology to Clostridium difficile ToxA (lif), and a small heat stable enterotoxin also found in enteroaggregative E.coli known as EAST (astA).

Genotypic profiling of 22 E.coli O157 strains isolated from human disease outbreaks, and 31 E.coli O157 strains isolated from asymptomatic cattle, demonstrated that all human outbreak isolates carried a stx2 or stx2c gene, whilst cattle isolates had no specific pattern to carriage of stx1 or stx2 genes. The genotypic profiling also showed that there was little heterogeneity in the carriage of the other toxin genes among human outbreak or bovine isolates. However phenotypic profiling demonstrated that there is a clear difference between human and bovine isolates in their ability to produce high levels of secreted protein in vitro. While the human outbreak isolates produced secreted proteins at high levels, this was true of only a subset of bovine isolates. Whether high level of Esp secretion correlates with human pathogenic potential remains to be determined.

University of Edinburgh, Dept of Veterinary Pathology, Medical Microbiology, Teviot Place, Edinburgh EH8 9AG
Tel: 0131 650 3155 Fax: 0131 650 6531 E-mail: 9907286@sms.ed.ac.uk

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