Serotypes and analysis of distribution of Shiga toxin-producing Escherichia coli from cattle and sheep in the lower North Island, New Zealand

Abstract

AIMS: To serotype a subset of Shiga toxin-producing Escherichia coli (STEC) isolates from cattle and sheep to determine whether any corresponding serotypes have been implicated in human diarrhoeal disease, both in New Zealand and worldwide, and to examine the distribution of STEC and enteropathogenic Escherichia coli (EPEC) amongst cattle (calves, heifers and dairy) and sheep (lambs, rams and ewes), to assess whether carriage of identified bacterial genotypes may be associated with a particular age of animal.

METHODS: Recto-anal mucosal swabs (RAMS) were taken from 91 calves, 24 heifers and 72 dairy cattle, and 46 lambs, 50 ewes and 36 rams, from four sites in the Manawatu and Rangitikei regions of New Zealand. Strains of E. coli selected from primary isolation plates were subjected to a multiplex polymerase chain reaction (PCR), to determine the presence of Shiga toxin genes (stx1 and stx2) and the E. coli attaching and effacing gene (eae).

RESULTS: Overall, 186/319 (58.3%) animals sampled were positive for stx1, stx2, or eae isolates. More sheep (43.9%) were stx1 -positive than cattle (2.7%; p=0.036), and amongst sheep more lambs and ewes were stx1 -positive than rams (p=0.036). Amongst cattle, more calves and heifers were eae-positive than dairy cows (p=0.030). Two or more different STEC were isolated from at least 28 (9%) animals (three cattle and 25 sheep), based on their stx/eae genotype. Enterohaemolysin genes were found in 39/51 (76%) isolates serotyped. Twenty-one different serotypes were detected, including O5:H-, O9:H51, O26:H11, O84:H-/H2 and O149:H8 from cattle, and O26:H11,O65:H-, O75:H8, O84:H-, O91:H-, O128:H2 and O174:H8 from sheep; O84:H-, O26:H11, O5:H-, O91:H- and O128:H2 serotypes have been associated with human disease.

CONCLUSIONS: If nationally representative, this study confirms that cattle and sheep in New Zealand may be a major reservoir of STEC serotypes that have been recognised as causative agents of diarrhoeal disease in humans. Distribution of STEC and EPEC in cattle and sheep indicates that direct contact with, in particular, calves or their faeces, or exposure to environments cross contaminated with ruminant faeces, may represent an increased risk factor for human disease in New Zealand.

KEY WORDS:

• STEC
• EPEC
• stx
• eae
• ruminant
• public health

Acknowledgements

We acknowledge the assistance of Steve Lees, Colin Faiers, Dan Robinson, Neville Grace, Scott Knowles, Jacalyn Scott and Graham McCool for animal sampling. We thank Zaneta Park-Ng for excellent statistical assistance. Sam Taylor was the recipient of an AgResearch Summer Studentship.