Abstract
The emergence of antibiotic-resistant bacteria has led to the need for a unifying One Health approach to optimise antibiotic use in agriculture and veterinary medicine. Escherichia coli is an important One Health pathogen due to its ubiquitous presence in the mammalian gastrointestinal tract and importance as an opportunistic human and animal pathogen. As part of the wider Arwain DGC project, aiming to reduce antibiotic use and improve antibiotic stewardship on Welsh farms, antibiotic resistance in E. coli was monitored on 33 farms with beef cattle and sheep over a period from 2022 to 2024. Here, we phenotypically and genotypically characterise antibiotic resistance in E. coli isolates to common veterinary antibiotics as well as antibiotics critical for human health. Additionally, due to the discontinuation of the only licensed treatment for watery mouth disease in lambs and the overlap of the industries rearing beef cattle and sheep, we monitored and characterised spectinomycin resistance in these animal populations. Overall, we observed no significant change in sample-level resistance to the monitored category C/D antibiotics over the two years in any of the farm or animal types. Resistance to the monitored, critically important antibiotics remained low, and there was a low-level presence of genotypic resistance to antibiotics important for treating human infections. While there was initially a considerable decrease in phenotypic spectinomycin resistance, we observed an eventual stabilisation. Using genomic analysis, we found the spectinomycin resistance gene aadA was carried on diverse strains and genetic elements, but typically on a Class 1 integron. These elements were often associated with the carriage of one or more additional resistance genes, potentially contributing to the co-selection of resistance. Frequently, resistance genes directly linked to aadA conferred resistance to beta-lactams and trimethoprim, but these elements were often associated with sulphonamide, tetracycline, and macrolide resistance. We observed an increase towards patterns containing amoxicillin/clavulanic acid resistance genes encoding CARB-2 and OXA, which we hypothesise is caused by changes in selective pressures due to the discontinuation. Using phylogenetic analysis, we found that there was some evidence of transfer of spectinomycin-resistant strains between farms, particularly within mixed farms, likely associated with the frequent movement of livestock associated with these systems. This work provides data on antibiotic resistance in less-studied beef and sheep production systems, and areas of focus for antibiotic stewardship forimproved prescribing.
| Date of Award | 9 Dec 2025 |
|---|---|
| Original language | English |
| Awarding Institution |
|
| Supervisor | Matthew B Avison (Supervisor) & Ruth C Massey (Supervisor) |