title: Cross-sectional study of antimicrobial-resistant bacteria in horses. Part 1: Prevalence of antimicrobial-resistant Escherichia coli and methicillin-resistant Staphylococcus aureus.
abstract: BACKGROUND
  The increasing prevalence of antimicrobial-resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA) and antimicrobial-resistant Escherichia coli represents a significant problem. However, the carriage of such bacteria by horses in the UK has not been well characterised.
  
  
  OBJECTIVE
  To estimate the prevalence of nasal carriage of MRSA and faecal carriage of antimicrobial-resistant E. coli amongst horses in the general equine community of the mainland UK.
  
  
  METHODS
  A cross-sectional study of horses recruited by 65 randomly selected equine veterinary practices was conducted, with nasal swabs and faecal samples collected. Faecal samples were cultured for antimicrobial-resistant E. coli. Nasal swabs were cultured for staphylococcal species; methicillin-resistant isolates identified as S. aureus were characterised by SCCmec and spa gene typing. Multilevel logistic regression models were used to calculate prevalence estimates with adjustment for clustering at practice and premises levels. Spatial variation in risk of antimicrobial resistance was also examined.
  
  
  RESULTS
  In total, 650 faecal samples and 678 nasal swabs were collected from 692 horses located on 525 premises. The prevalence of faecal carriage of E. coli with resistance to any antimicrobial was 69.5% (95% CI 65.9-73.1%) and the prevalence of extended-spectrum β-lactamase (ESBL)-producing E. coli was 6.3% (95% CI 4.1-9.6%). The prevalence of nasal carriage of MRSA was 0.6% (95% CI 0.2-1.5%). Spatial analysis indicated variation across the UK for risk of carriage of resistant and multidrug-resistant (resistant to more than 3 antimicrobial classes) E. coli.
  
  
  CONCLUSIONS
  Carriage of MRSA by horses in the community appears rare, but the prevalence of antimicrobial-resistant E. coli (including ESBL-producing E. coli) is higher. A high prevalence of antimicrobial-resistant bacteria could have significant health implications for the horse population of the UK.
authors.affiliation: National Centre for Zoonosis Research, School of Veterinary Sciences, Leahurst Campus, University of Liverpool, UK. thomas.maddox@liverpool.ac.uk
authors.forename: T W
authors.initials: TW
authors.lastname: Maddox
authors.forename: P D
authors.initials: PD
authors.lastname: Clegg
authors.forename: P J
authors.initials: PJ
authors.lastname: Diggle
authors.forename: A L
authors.initials: AL
authors.lastname: Wedley
authors.forename: S
authors.initials: S
authors.lastname: Dawson
authors.forename: G L
authors.initials: GL
authors.lastname: Pinchbeck
authors.forename: N J
authors.initials: NJ
authors.lastname: Williams
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002353:Carrier State / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary; D003430:Cross-Sectional Studies; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000187:drug effects* / Q000302:isolation & purification; D004927:Escherichia coli Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D005243:Feces / Q000382:microbiology; D005260:Female; D006734:Horse Diseases / Q000453:epidemiology / Q000382:microbiology*; D006736:Horses; D008297:Male; D016106:Methicillin Resistance; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects / Q000302:isolation & purification*; D009297:Nasal Mucosa / Q000382:microbiology; D015995:Prevalence; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000382:microbiology / Q000662:veterinary*; D006113:United Kingdom / Q000453:epidemiology
chemical_list: D000900:Anti-Bacterial Agents