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Applied and Environmental Microbiology, October 2008, p. 6378-6384, Vol. 74, No. 20
0099-2240/08/$08.00+0     doi:10.1128/AEM.00636-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Early Attachment Sites for Shiga-Toxigenic Escherichia coli O157:H7 in Experimentally Inoculated Weaned Calves{triangledown}

Evelyn A. Dean-Nystrom,1* William C. Stoffregen,1,{ddagger} Brad T. Bosworth,1,§ Harley W. Moon,2 and Joachim F. Pohlenz1,{dagger}

Pre-Harvest Food Safety and Enteric Diseases Research Unit, National Animal Disease Center, Agricultural Research Service, U.S. Department of Agriculture, Ames, Iowa 50010,1 Veterinary Medical Research Institute, College of Veterinary Medicine, Iowa State University, Ames, Iowa 500112

Received 14 March 2008/ Accepted 14 August 2008

Weaned 3- to 4-month-old calves were fasted for 48 h, inoculated with 1010 CFU of Shiga toxin-positive Escherichia coli (STEC) O157:H7 strain 86-24 (STEC O157) or STEC O91:H21 strain B2F1 (STEC O91), Shiga toxin-negative E. coli O157:H7 strain 87-23 (Stx– O157), or a nonpathogenic control E. coli strain, necropsied 4 days postinoculation, and examined bacteriologically and histologically. Some calves were treated with dexamethasone (DEX) for 5 days (3 days before, on the day of, and 1 day after inoculation). STEC O157 bacteria were recovered from feces, intestines, or gall bladders of 74% (40/55) of calves 4 days after they were inoculated with STEC O157. Colon and cecum were sites from which inoculum-type bacteria were most often recovered. Histologic lesions of attaching-and-effacing (A/E) O157+ bacteria were observed in 69% (38/55) of the STEC O157-inoculated calves. Rectum, ileocecal valve, and distal colon were sites most likely to contain A/E O157+ bacteria. Fecal and intestinal levels of STEC O157 bacteria were significantly higher and A/E O157+ bacteria were more common in DEX-treated calves than in nontreated calves inoculated with STEC O157. Fecal STEC O157 levels were significantly higher than Stx– O157, STEC O91, or control E. coli; only STEC O157 cells were recovered from tissues. Identifying the rectum, ileocecal valve, and distal colon as early STEC O157 colonization sites and finding that DEX treatment enhances the susceptibility of weaned calves to STEC O157 colonization will facilitate the identification and evaluation of interventions aimed at reducing STEC O157 infection in cattle.

* Corresponding author. Mailing address: Pre-Harvest Food Safety and Enteric Diseases Research Unit, USDA, ARS, National Animal Disease Center, P.O. Box 70, Ames, IA 50010. Phone: (515) 663-7376. Fax: (515) 663-7458. E-mail: evelyn.nystrom{at}ars.usda.gov

{triangledown} Published ahead of print on 22 August 2008.

{ddagger} Present address: Boston Scientific Corporation, 5905 Nathan Lane, Plymouth, MN 55442.

§ Present address: Iowa State University, Ames, IA 50011.

{dagger} Deceased 10 January 2006. His enthusiasm for and contributions to this research are greatly missed.

Applied and Environmental Microbiology, October 2008, p. 6378-6384, Vol. 74, No. 20
0099-2240/08/$08.00+0     doi:10.1128/AEM.00636-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.





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