Abstract/Summary

The growing prevalence of antimicrobial resistance (AMR) by bacteria is a concern for both human and animal health. Escherichia coli (E. coli), found in the intestinal tracts of all animals and birds, has been widely used as a sentinel species for the determination of AMR. Antioxidants such as selenium and beneficial microbes such as yeasts and lactic acid bacteria may help prevent the proliferation of pathogenic bacteria and potentially AMR in the gut through mechanisms such as competitive exclusion, neutralization of toxins, bactericidal activity or enhanced immune competence. The aim of this study was to determine the evolution of AMR and virulence associated gene (VAG) of E. coli isolated from the caecum taken throughout the life of broiler chickens, and how this is influenced by administration of selenium, lactic acid bacteria and yeast. No antibiotics were administered to the birds at any time. There was no significant effect of either selenium or yeasts or lactic acid bacteria on the prevalence of AMR and VAG in these studies. The birds were most susceptible to antibiotic resistant infection (78.57% and 100% of E. coli colony forming units showing resistance to TET and AMP) at the end of the starter phase (around 8 days old). The carriage of AMR and VAG by E. coli then declined during the grower and finisher phases. However, in the final bird study, resistance by E. coli to ampicillin (ranging from 60.4% to 71.8%) and tetracycline (ranging from 89.0% to 99.4%) was maintained throughout the birds’ life, but the prevalence of VAG did decrease (being between 11.1% and 44.4% when birds were 28 days of age). The evolution of E. coli as the birds got older tended toward more commensal E. coli that were susceptible to antibiotics. The ability of E. coli to utilise sucrose, sorbose and dulcitol was associated with the carriage of VAG. Furthermore, AMR was associated with iron-uptake related genes. This suggests that further work investigating the manipulation of nutrient and iron availability in the chicken gut might provide a means of controlling the proliferation of putative pathogenic and AMR coliforms in young broiler chickens.