Molecular epidemiology of antimicrobial-resistant commensal Escherichia coli strains in a cohort of newborn calves

Deborah Hoyle, Catherine M Yates, Margo E Chase-Topping, Esther J Turner, Sarah E Davies, J Chris Low, George J. Gunn, Mark E J Woolhouse, Sebastian Amyes

Research output: Contribution to journalArticlepeer-review

Abstract

Pulsed-field gel electrophoresis (PFGE) was used to investigate the dissemination and diversity of ampicillin-resistant (Amp(r)) and nalidixic acid-resistant (Nal(r)) commensal Escherichia coli strains in a cohort of 48 newborn calves. Calves were sampled weekly from birth for up to 21 weeks and a single resistant isolate selected from positive samples for genotyping and further phenotypic characterization. The Amp(r) population showed the greatest diversity, with a total of 56 different genotype patterns identified, of which 5 predominated, while the Nal(r) population appeared to be largely clonal, with over 97% of isolates belonging to just two different PFGE patterns. Distinct temporal trends were identified in the distribution of several Amp(r) genotypes across the cohort, with certain patterns predominating at different points in the study. Cumulative recognition of new Amp(r) genotypes within the cohort was biphasic, with a turning point coinciding with the housing of the cohort midway through the study, suggesting that colonizing strains were from an environmental source on the farm. Multiply resistant isolates dominated the collection, with >95% of isolates showing resistance to at least two additional antimicrobials. Carriage of resistance to streptomycin, sulfamethoxazole, and tetracycline was the most common combination, found across several different genotypes, suggesting the possible spread of a common resistance element across multiple strains. The proportion of Amp(r) isolates carrying sulfamethoxazole resistance increased significantly over the study period (P < 0.05), coinciding with a decline in the most common genotype pattern. These data indicate that calves were colonized by a succession of multiply resistant strains, with a probable environmental source, that disseminated through the cohort over time.
Original languageEnglish
Pages (from-to)6680-8
Number of pages9
JournalApplied and Environmental Microbiology
Volume71
Issue number11
DOIs
Publication statusPublished - Nov 2005

Keywords

  • Ampicillin/pharmacology
  • Animals
  • Animals, Newborn
  • Anti-Bacterial Agents/pharmacology
  • Cattle/microbiology
  • Drug Resistance, Bacterial/genetics
  • Electrophoresis, Gel, Pulsed-Field
  • Escherichia coli/classification
  • Escherichia coli/genetics
  • Genotype
  • Microbial Sensitivity Tests
  • Molecular Epidemiology
  • Nalidixic Acid/pharmacology

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