Cross-sectional study of antimicrobial-resistant bacteria in horses. Part 1: Prevalence of antimicrobial-resistant Escherichia coli and methicillin-resistant Staphylococcus aureus.

REASONS FOR PERFORMING STUDY: 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. OBJECTIVES: 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 ß-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 AND POTENTIAL RELEVANCE: 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.

Cross-sectional study of antimicrobial-resistant bacteria in horses. Part 2: Risk factors for faecal carriage of antimicrobial-resistant Escherichia coli in horses.

REASONS FOR PERFORMING STUDY: The increasing prevalence of antimicrobial resistant bacteria such as antimicrobial-resistant and extended spectrum ß-lactamase (ESBL)-producing Escherichia coli represents a significant problem for human and veterinary medicine. Despite this, the risk factors for faecal carriage of such bacteria by horses in the UK, particularly those in the wider community, have not been well described. OBJECTIVES: To characterise the risk factors for faecal carriage of antimicrobial-resistant E. coli amongst horses in the mainland UK. METHODS: A cross-sectional study of horses recruited by 65 randomly selected equine veterinary practices was conducted, with a faecal sample collected and self-administered questionnaire completed by the horse owner. Faecal samples were cultured for antimicrobial-resistant E. coli, with isolates confirmed as E. coli having their antimicrobial resistance profile determined. Multilevel, multivariable logistic regression models were used to investigate risk factors for the carriage of antimicrobial-resistant E. coli in the sample population. RESULTS: Faecal samples and completed questionnaires were obtained for 627 horses located on 475 premises. Recent hospitalisation, contact with specific types of nonequid animals, the type of premises, the surrounding land use, the reason for veterinary treatment received in the last 6 months and antimicrobial treatment in the previous 10 days were identified as risk factors for many of the antimicrobial-resistance outcomes considered. Being stabled on the same yard as a recently hospitalised horse was identified as a risk factor for increased risk of carriage of ESBL-producing E. coli. CONCLUSIONS AND POTENTIAL RELEVANCE: Increasing antimicrobial resistance may have significant health implications for the horse population of Great Britain. This form of epidemiological investigation highlights potential risk factors that may be controlled to limit the extent of the problem.

Prevalence of antimicrobial-resistant Escherichia coli in dogs in a cross-sectional, community-based study.

The prevalence of carriage of antimicrobial-resistant (AMR) and extended-spectrum ß-lactamase (ESBL)-producing Escherichia coli was determined in 183 healthy dogs from a semi-rural community in Cheshire. Isolates were tested against a panel of antimicrobials and by PCR to detect resistance genes. In the suspected ESBL-producing isolates, the presence of bla(SHV), bla(TEM), bla(CTX-M) and bla(AmpC) genes was determined by PCR and sequencing. A total of 53 (29 per cent, 95 per cent confidence interval [CI] 22.4 to 35.5 per cent) dogs carried at least one AMR E coli isolate. Twenty-four per cent (95 per cent CI 17.9 to 30.2 per cent) of dogs carried isolates resistant to ampicillin, 19.7 per cent (95 per cent CI 13.9 to 25.4 per cent) to tetracycline and 16.9 per cent (95 per cent CI 11.5 to 22.4 per cent) to trimethoprim. A bla(TEM) gene was detected in 39 of 54 ampicillin-resistant isolates, a tet(B) gene in 12 of 45 tetracycline-resistant isolates, and a dfr gene in 22 of 33 trimethoprim-resistant isolates. Multidrug-resistant isolates were demonstrated in 15 per cent (28 of 183; 95 per cent CI 10.1 to 20.5 per cent) of dogs. Nine suspected ESBL-producing E coli were isolated, of which only one was confirmed by double disc diffusion testing. Two of these isolates carried the bla(TEM-1) gene and seven carried the bla(CMY-2) gene.