How to cite this article: Vet. Res. (2009) 40:09
DOI: 10.1051/vetres:2008047

Intermittent Escherichia coli O157:H7 colonisation at the terminal rectum mucosa of conventionally-reared lambs

Angus Best¹, Derek Clifford², Bentley Crudgington³, William A. Cooley⁴, Alejandro Nunez³, Ben Carter⁵, Ute Weyer², Martin J. Woodward¹ and Roberto M. La Ragione<sup>1

1</sup>  Department of Food and Environmental Safety, Veterinary Laboratories Agency (VLA), Weybridge, Woodham Lane, New Haw, Addlestone, Surrey, KT15 3NB, United Kingdom
²  Animal Services Unit, Veterinary Laboratories Agency (VLA), Weybridge, Woodham Lane, New Haw, Addlestone, Surrey, KT15 3NB, United Kingdom
³  Department of Pathology, Veterinary Laboratories Agency (VLA), Weybridge, Woodham Lane, New Haw, Addlestone, Surrey, KT15 3NB, United Kingdom
⁴  Department of Molecular Pathogenesis and Genetics, Veterinary Laboratories Agency (VLA), Weybridge, Woodham Lane, New Haw, Addlestone, Surrey, KT15 3NB, United Kingdom
⁵  South East Wales Trials Unit, Neuadd Meirionnydd, School of Medicine, Heath Park, Cardiff University, CF14 4XN, United Kingdom

Received 9 April 2008; accepted 28 October 2008; published online 30 October 2008

Abstract - In cattle, the lymphoid rich regions of the rectal-anal mucosa at the terminal rectum are the preferred site for Escherichia coli O157:H7 colonisation. All cattle infected by rectal swab administration demonstrate long-term E. coli O157:H7 colonisation, whereas orally challenged cattle do not demonstrate long-term E. coli O157:H7 colonisation in all animals. Oral, but not rectal challenge of sheep with E. coli O157:H7 has been reported, but an exact site for colonisation in sheep is unknown. To determine if E. coli O157:H7 can effectively colonise the ovine terminal rectum, in vitro organ culture (IVOC) was initiated. Albeit sparsely, large, densely packed E. coli O157:H7 micro-colonies were observed on the mucosa of ovine and control bovine terminal rectum explants. After necropsy of orally inoculated lambs, bacterial enumeration of the proximal and distal gastrointestinal tract did suggest a preference for E. coli O157:H7 colonisation at the ovine terminal rectum, albeit for both lymphoid rich and non-lymphoid sites. As reported for cattle, rectal inoculation studies were then conducted to determine if all lambs would demonstrate persistent colonisation at the terminal rectum. After necropsy of E. coli O157:H7 rectally inoculated lambs, most animals were not colonised at gastrointestinal sites proximal to the rectum, however, large densely packed micro-colonies of E. coli O157:H7 were observed on the ovine terminal rectum mucosa. Nevertheless, at the end point of the study (day 14), only one lamb had E. coli O157:H7 micro-colonies associated with the terminal rectum mucosa. A comparison of E. coli O157:H7 shedding yielded a similar pattern of persistence between rectally and orally inoculated lambs. The inability of E. coli O157:H7 to effectively colonise the terminal rectum mucosa of all rectally inoculated sheep in the long term, suggests that E. coli O157:H7 may colonise this site, but less effectively than reported previously for cattle.

Key words: E. coli O157:H7 / IVOC / lymphoid / terminal rectum / ovine

Corresponding author: a.best@vla.defra.gsi.gov.uk

© INRA, EDP Sciences 2009