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Applied and Environmental Microbiology, November 2008, p. 6956-6962, Vol. 74, No. 22
0099-2240/08/$08.00+0     doi:10.1128/AEM.01241-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Effects of Therapeutic Ceftiofur Administration to Dairy Cattle on Escherichia coli Dynamics in the Intestinal Tract{triangledown} ,{dagger}

Randall S. Singer,1,2* Sheila K. Patterson,2 and Richard L. Wallace3

Department of Veterinary and Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, St. Paul, Minnesota 55108,1 Department of Veterinary Pathobiology, College of Veterinary Medicine, University of Illinois, Urbana, Illinois 61802,2 Department of Veterinary Clinical Medicine, College of Veterinary Medicine, University of Illinois, Urbana, Illinois 618023

Received 4 June 2008/ Accepted 18 September 2008

The goal of this study was to follow ceftiofur-treated and untreated cattle in a normally functioning dairy to examine enteric Escherichia coli for changes in antibiotic resistance profiles and genetic diversity. Prior to treatment, all of the bacteria cultured from the cows were susceptible to ceftiofur. Ceftiofur-resistant E. coli was only isolated from treated cows during and immediately following the cessation of treatment, and the 12 blaCMY-2-positive isolates clustered into two genetic groups. E. coli bacterial counts dropped significantly in the treated animals (P < 0.027), reflecting a disappearance of the antibiotic-susceptible strains. The resistant bacterial population, however, did not increase in quantity within the treated cows; levels stayed low and were overtaken by a returning susceptible population. There was no difference in the genetic diversities of the E. coli between the treated and untreated cows prior to ceftiofur administration or after the susceptible population of E. coli returned in the treated cows. A cluster analysis of antibiotic susceptibility profiles resulted in six clusters, two of which were multidrug resistant and were comprised solely of isolates from the treated cows immediately following treatment. The antibiotic treatment provided a window to detect the presence of ceftiofur-resistant E. coli but did not appear to cause its emergence or result in its amplification. The finding of resistant isolates following antibiotic treatment is not sufficient to estimate the strength of selection pressure nor is it sufficient to demonstrate a causal link between antibiotic use and the emergence or amplification of resistance.

* Corresponding author. Mailing address: Department of Veterinary and Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, 300A VSB, 1971 Commonwealth Avenue, St. Paul, MN 55108. Phone: (612) 625-6271. Fax: (612) 625-5203. E-mail: singe024{at}umn.edu

{triangledown} Published ahead of print on 26 September 2008.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, November 2008, p. 6956-6962, Vol. 74, No. 22
0099-2240/08/$08.00+0     doi:10.1128/AEM.01241-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Carattoli, A. (2009). Resistance Plasmid Families in Enterobacteriaceae. Antimicrob. Agents Chemother. 53: 2227-2238 [Full Text]  
  • Daniels, J. B., Call, D. R., Hancock, D., Sischo, W. M., Baker, K., Besser, T. E. (2009). Role of Ceftiofur in Selection and Dissemination of blaCMY-2-Mediated Cephalosporin Resistance in Salmonella enterica and Commensal Escherichia coli Isolates from Cattle. Appl. Environ. Microbiol. 75: 3648-3655 [Abstract] [Full Text]  


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