Characterisation and clonal relationships of Shiga-toxigenic Escherichia coli (STEC) isolated from Australian dairy cattle

A total of 136 Shiga toxin-producing Escherichia coli (STEC) isolated durin g a longitudinal survey of three Australian dairy farms were examined to de termine their virulence factors, serotype and genomic relationships. This s tudy aimed to assess the potential of these STEC to cause disease in humans and to analyse the on-farm ecology of STEC. Virulence factors (sis, eae, e hxA) were used as determinants of potential to be enterohaemorrhagic E. col i (EHEC) and were examined using polymerase chain reaction (PCR). Among the cattle groups tested, calves, both before and during weaning, shed the mos t putative EHEC and were the main source of serotypes commonly associated w ith human disease. E, coli O157:H7 and E, coli O26:H11 represented 9.4 and 7.8% of cattle STEC isolates respectively, with other putative EHEC serotyp es reported for the first time from cattle. Based on serotype and virulence factors, 20% of STEC were putative EHEC. Pulsed-field gel electrophoresis (PFGE) was used to compare the genomic profiles of STEC from dairy farms. I solates common to cattle and the farm environment were identified. Multiple strains of STEC with high clonal turnover were detected in the faeces of c attle, and isolates appeared to be specific to individual farms. To fully a ssess the pre-slaughter EHEC risk factors on-farm, examination of STEC viru lence is as important as determination of STEC prevalence. (C) 2001 Elsevie r Science B.V. All rights reserved.