Influence of Therapeutic Ceftiofur Treatments of Feedlot Cattle on Fecal and Hide Prevalences of Commensal Escherichia coli Resistant to Expanded-Spectrum Cephalosporins, and Molecular Characterization of Resistant Isolates

Authors

John W. Schmidt, U.S. Department of AgricultureFollow
Dee Griffin, University of Nebraska - LincolnFollow
Larry A. Kuehn, U.S. Department of AgricultureFollow
Dayna M. Brichta-Harhay, U.S. Department of AgricultureFollow

Date of this Version

2013

Citation

Published in Applied and Environmental Microbiology (2013) 79:7, p. 2273-2283. DOI:10.1128/AEM.03592-12

Comments

Copyright © 2013 American Society for Microbiology

Abstract

In the United States, the bla_CMY-2 gene contained within incompatibility type A/C (IncA/C) plasmids is frequently identified in extended-spectrum-cephalosporin-resistant (ESC^r) Escherichia coli strains from both human and cattle sources. Concerns have been raised that therapeutic use of ceftiofur in cattle may increase the prevalence of ESC^r E. coli. We report that herd ESC^r E. coli fecal and hide prevalences throughout the residency of cattle at a feedlot, including during the period of greatest ceftiofur use at the feedlot, were either not significantly different (P≥0.05) or significantly less (Pr E. coli shedding that follows ceftiofur injection abated, ceftiofur-injected cattle were no more likely than untreated members of the same herd to shed ESC^r E. coli. Pulsed-field gel electrophoresis (PFGE) genotyping, antibiotic resistance phenotyping, screening for presence of the bla_CMY-2 gene, and plasmid replicon typing were performed on 312 ESC^r E. coli isolates obtained during six sampling periods spanning the 10-month residence of cattle at the feedlot. The identification of only 26 unique PFGE genotypes, 12 of which were isolated during multiple sampling periods, suggests that clonal expansion of feedlot-adapted bla_CMY-2 E. coli strains contributed more to the persistence of bla_CMY-2 than horizontal transfer of IncA/C plasmids between E. coli strains at this feedlot. We conclude that therapeutic use of ceftiofur at this cattle feedlot did not significantly increase the herd prevalence of ESC^r E. coli.