Molecular characterisation of bovine faecal Escherichia coli shows persistence of defined ampicillin resistant strains and the presence of class 1 integrons on an organic beef farm

Vet Microbiol. 2006 Jun 15;115(1-3):250-7. doi: 10.1016/j.vetmic.2006.01.006. Epub 2006 Feb 21.


Antimicrobial use is heavily restricted on organic farms; however, few studies have been conducted to investigate the impact this has on the epidemiology of resistance in pathogenic and commensal bacteria. We investigated the persistence of antimicrobial resistant Escherichia coli within an organic beef herd over a period of 28 months. Faecal samples collected monthly from three calf cohorts and annually from adult cattle and environmental samples, were screened for the presence of ampicillin, apramycin and nalidixic acid resistant E. coli. The prevalence of ampicillin resistance ranged from 27.3 to 40.7% in the annual herd and environmental samplings (n=22-55) and was greater in the calf cohorts, with a peak cohort prevalence of >47% in all 3 years (n=16-18). Apramycin and nalidixic acid resistant E. coli were rare. Pulsed-field gel electrophoresis (PFGE) identified 10 main genotype groups within the herd, with evidence of strain transmission between different livestock groups, animal species and years. Multiple resistance was found in >44% of isolates tested, with ampicillin, neomycin, sulphamethoxazole and tetracycline carriage the commonest phenotype identified. PCR detected the presence of class 1 integrons in <5% of resistant isolates, 6/7 of which were of cattle origin. These data demonstrate that ampicillin resistant E. coli was common on the farm despite restricted antimicrobial use, although strain diversity was low. Persistence of defined genotype groups was observed between years, together with the transmission of resistant strains between different animal species on the farm.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Agriculture / methods*
  • Ampicillin Resistance*
  • Animals
  • Anti-Bacterial Agents / pharmacology*
  • Anti-Bacterial Agents / therapeutic use
  • Cattle
  • Cattle Diseases / drug therapy*
  • Cattle Diseases / microbiology
  • Cattle Diseases / transmission
  • Cohort Studies
  • Drug Resistance, Multiple, Bacterial
  • Electrophoresis, Gel, Pulsed-Field
  • Environmental Microbiology
  • Escherichia coli / classification
  • Escherichia coli / drug effects*
  • Escherichia coli / genetics
  • Escherichia coli Infections / drug therapy
  • Escherichia coli Infections / microbiology
  • Escherichia coli Infections / transmission
  • Escherichia coli Infections / veterinary*
  • Feces / microbiology
  • Genotype
  • Integrons
  • Microbial Sensitivity Tests / veterinary
  • Polymerase Chain Reaction / veterinary
  • Prevalence
  • Species Specificity


  • Anti-Bacterial Agents