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Applied and Environmental Microbiology, June 2009, p. 3648-3655, Vol. 75, No. 11
0099-2240/09/$08.00+0     doi:10.1128/AEM.02435-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Role of Ceftiofur in Selection and Dissemination of bla_CMY-2-Mediated Cephalosporin Resistance in Salmonella enterica and Commensal Escherichia coli Isolates from Cattle

Joshua B. Daniels,¹ Douglas R. Call,¹ Dale Hancock,² William M. Sischo,² Katherine Baker,² and Thomas E. Besser^1*

Department of Veterinary Microbiology and Pathology, Washington State University College of Veterinary Medicine, Pullman, Washington 99164,¹ Department of Veterinary Clinical Sciences, Washington State University College of Veterinary Medicine, Pullman, Washington 99164²

Received 23 October 2008/ Accepted 3 April 2009

Third-generation cephalosporin resistance of Salmonella and commensal Escherichia coli isolates from cattle in the United States is predominantly conferred by the cephamycinase CMY-2, which inactivates β-lactam antimicrobial drugs used to treat a wide variety of infections, including pediatric salmonellosis. The emergence and dissemination of bla_CMY-2--bearing plasmids followed and may in part be the result of selection pressure imposed by the widespread utilization of ceftiofur, a third-generation veterinary cephalosporin. This study assessed the potential effects of ceftiofur on bla_CMY-2 transfer and dissemination by (i) an in vivo experimental study in which calves were inoculated with competent bla_CMY-2-bearing plasmid donors and susceptible recipients and then subjected to ceftiofur selection and (ii) an observational study to determine whether ceftiofur use in dairy herds is associated with the occurrence and frequency of cephalosporin resistance in Salmonella and commensal E. coli. The first study revealed bla_CMY-2 plasmid transfer in both ceftiofur-treated and untreated calves but detected no enhancement of plasmid transfer associated with ceftiofur treatment. The second study detected no association (P = 0.22) between ceftiofur use and either the occurrence of ceftiofur-resistant salmonellosis or the frequency of cephalosporin resistance in commensal E. coli. However, herds with a history of salmonellosis (including both ceftiofur-resistant and ceftiofur-susceptible Salmonella isolates) used more ceftiofur than herds with no history of salmonellosis (P = 0.03) These findings fail to support a major role for ceftiofur use in the maintenance and dissemination of bla_CMY-2-bearing plasmid mediated cephalosporin resistance in commensal E. coli and in pathogenic Salmonella in these dairy cattle populations.

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* Corresponding author. Mailing address: Department of Veterinary Microbiology and Pathology, Washington State University College of Veterinary Medicine, P.O. Box 647040, Pullman, WA 99164. Phone: (509) 335-6075. Fax: (509) 335-8529. E-mail: tbesser{at}vetmed.wsu.edu

Published ahead of print on 17 April 2009.

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Applied and Environmental Microbiology, June 2009, p. 3648-3655, Vol. 75, No. 11
0099-2240/09/$08.00+0     doi:10.1128/AEM.02435-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.