Carriage of antimicrobial-resistant Escherichia coli and Staphylococci in dogs in the community : molecular mechanisms

While previous studies have determined the prevalence of meticillin resistant Staphylococcus aureus (MRSA) and antimicrobial resistant (AMR) Escherichia coli in canine populations, few have included sufficiently large sample sizes and fewer still have characterised the isolates or investigated risk factors that might be associated with their carriage. The main aims of the work presented in this thesis were; to determine the nasal prevalence of MRSA and other AMR staphylococci and the faecal prevalence of AMR E. coli in faeces in the canine population of mainland UK. The study also aimed to characterise the bacteria isolated using molecular techniques in order for comparisons to be made with isolates of human origin, and to determine the presence of potential risk factors associated with faecal carriage of AMR E. coli. These objectives were achieved by carrying out two studies. The first study used frozen canine faecal samples collected during a cross sectional study of a semi-rural community in Cheshire to determine the prevalence of AMR E. coli. The second study collected faecal and nasal swabs from dogs visiting veterinary practices across mainland UK. Antimicrobial resistance of the isolates obtained from both studies were characterised using disc diffusion methods and PCR assays. In addition, isolates collected during the second study were subjected to multi-locus sequence typing and DNA micro array analysis of resistance and virulence genes. For antimicrobial resistant E. coli, risk factors associated with carriage were investigated. The prevalence of MRSA in the canine population was found to be low at 1% and all isolates were identical to EMRSA-15, the main human endemic strain in many UK hospitals. The overall S. aureus prevalence was 7.5%, with a higher prevalence of 11.0% of S. pseudintermedius, in which no meticillin resistance was found. Meticillin resistant coagulase negative Staphylococcus spp. was found in 5.5% of dogs. AMR in the isolates varied between species; however resistance to fusidic acid was consistently high. AMR E. coli was common in both studies (29.0% in community study and 44.8% in nationwide study). Resistance to ampicillin (24.0% and 37.2%), tetracycline (19.7% and 30.0%), trimethoprim (16.9% and 23.8%) and resistance to three or more antimicrobial classes (15.3% and 18.1%) was found to be high in both studies (community and nationwide respectively), while resistance to augmentin, chloramphenicol, ciprofloxacin and nalidixic acid was below 10% in both studies. A variety of genes responsible for resistance to expanded spectrum β-lactams was identified; including blaCTX-M-15 and blacmy2, both of which have previously been identified in humans and dogs. A number of variables were found to be associated with resistance to antimicrobials, with previous prescription of antimicrobials and consumption of raw poultry meat remaining in the final model of more than one resistance outcome. The carriage of MRSA and antimicrobial resistant E. coli could pose a potential problem both in terms of the welfare of the dogs carrying such bacteria as well as the zoonotic potential of the bacteria and resistance determinants.