Wild birds as a reservoir of antimicrobial resistance (AMR) in the environment

Antimicrobial resistance (AMR) is one of the greatest public health threats and has been conceptualised as a slowly emerging disaster. Studies have suggested that wild birds contribute as a reservoir and dispersal route of AMR, and proximity to anthropogenic activity has been associated with higher prevalence of AMR. This study was conducted to determine the prevalence and diversity of extended-spectrum ?-lactam (ESBL) resistant coliforms in wild bird populations in Scotland across a gradient of anthropogenic activity. Two bird taxa with functional differences were selected: gulls and geese and sampled across areas of different anthropogenic activity: urban and rural. A total of 226 bird faecal samples (47 gull faeces from a waste water treatment works (WWTW), 50 gull faeces from a rural site, 77 goose faeces from city lochs and 52 goose faeces from a rural site) were screened using a selective media. To determine diversity of isolates, up to 10 resistant and sensitive colonies from each sample were selected and tested using REP-PCR. One isolate from each REP type was selected for further characterisation including E. coli strain diversity, phylo-groups, sequence type (ST), susceptibility testing and resistance genes. This study found a significantly higher prevalence of ESBL-producer E. coli (57% urban vs 2% rural) and ESBL-producer non-E. coli coliforms (32% urban vs 4% rural) in gulls at the urban site compared to the rural site. The difference in the prevalence of ESBL-producer non-E. coli coliforms in geese in the urban (5%) and rural (17%) sites was not statistically significant. Of 33 E. coli REP types identified, 88% were distinctly carried by birds. Six phylo-groups and one cryptic clade were detected, and the phylo-group B1 was the most prevalent. Multi-drug resistant (resistance ? 3 antibiotic classes) E. coli were only found in gulls at the WWTW (urban site). The most common ESBL-producer gene in this study was blaCTX-M group 1. This study suggests that gulls feeding on a WWTW site have a major role as a reservoir of AMR, whereas geese in urban lochs and migratory geese have a minor role.