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Impact of the Direct Application of Therapeutic Agents to the Terminal Recta of Experimentally Colonized Calves on Escherichia coli O157:H7 Shedding

Animal Health Group, Scottish Agricultural College, West Mains Road, Edinburgh EH9 3JG, United Kingdom,¹ Centre for Infectious Diseases, Chancellor's Building, University of Edinburgh, 49 Little France Crescent, Edinburgh EH16 4SB, United Kingdom,² Biomathematics & Statistics Scotland, The King's Buildings, Edinburgh EH9 3JZ, United Kingdom³

Received 24 July 2006/ Accepted 28 December 2006

Enterohemorrhagic Escherichia coli O157:H7 is an important intestinal pathogen of humans with a main reservoir of domesticated ruminants, particularly cattle. It is anticipated that the risk of human infection can be reduced by controlling the organism within its reservoir hosts. Several options for the control of E. coli O157:H7 in cattle have been proposed, but none have been demonstrated to be successful in the field. Here we describe a novel experimental method, based on the terminal-rectum-restricted colonization described previously, to eliminate fecal carriage of E. coli O157:H7. In experimentally challenged calves, direct application to the rectal mucosa of either of two therapeutic agents, polymyxin B or chlorhexidine, greatly reduced bacterial shedding levels in the immediate posttreatment period. The most efficacious therapeutic agent, chlorhexidine, was compared in orally and rectally challenged calves. The treatment eliminated high-level shedding and reduced low-level shedding by killing bacteria at the terminal rectum. A rapid-detection system based on the ability to identify E. coli O157:H7 from swabs of the rectal mucosa was also assessed. This test was sufficiently sensitive to identify high-level bacterial carriage. Thus, a combination of the detection method and treatment regimens could be used in the field to eliminate high-level fecal excretion of E. coli O157:H7, so greatly reducing its prevalence within this host and the risk of human infection.

Published ahead of print on 12 January 2007.