Doctoral Thesis
Epidemiology of antimicrobial resistance in the Australia dairy cattle industry
Doctor of Philosophy (PhD), Murdoch University
2024
Abstract
Antimicrobials are essential for the management and treatment of disease. However, a risk of developing antimicrobial resistance (AMR) is associated with antimicrobial use (AMU). A multifaceted study was conducted to understand the epidemiology of AMR within the Australian dairy cattle industry. This included the risk assessment of industry AMR through a scoping review of ad hoc surveillance articles, alongside surveys to assess dairy veterinarian antimicrobial prescription patterns and the AMU practices of dairy farmers. A cross-sectional study to determine population level AMR was then conducted and a targeted approach to identify extended spectrum β-lactamase (ESBL) and AmpC β-lactamase (AmpC) producing commensal Escherichia coli developed.
It was identified that the health and age status of the sampled animals impacted on the prevalence of phenotypic AMR, as per the data presented across the 29 articles identified to meet the scoping review study criteria. Dairy veterinarians had a high agreement regarding label indications (96%), consequences of off-label prescription (95%), and the presence of an AMR risk (73%), when prescribing antimicrobials. On-farm practices in relation to AMU and treatment “always” or “often” stocking antimicrobials on-farm (> 50%) and disease treatment by farm staff (> 41%) across six main common dairy cattle conditions. The prevalence of clinical resistance was low across the eight antimicrobials investigated, being higher for calves than for lactating cows, while the prevalence of NWT commensal E. coli was highest for ampicillin from both source populations, being 68.8% (95% CI = 64.7 – 72.7) and 67.1% (95% CI = 62.0 – 72.0) for lactating cow and calf faeces respectively. The overall prevalence of ESBL/AmpC producing commensal E. coli was 7.3%, being 3.2% for isolates from lactating cow faeces and 12.7% for isolates from calf faeces. In conclusion, while the prevalence of clinical AMR was low, the presence of ‘non-wild type’ commensal E. coli and the presence of AMR genes implies AMR risk within the industry. These findings provide considerable knowledge to inform AMR risk reduction policy and maintain antimicrobial efficiency within the Australian dairy industry.
Details
- Title
- Epidemiology of antimicrobial resistance in the Australia dairy cattle industry
- Authors/Creators
- Michele Tree
- Contributors
- Anne Barnes (Supervisor) - Murdoch University, Centre for Animal Production and Health
- Awarding Institution
- Murdoch University; Doctor of Philosophy (PhD)
- Identifiers
- 991005726582907891
- Murdoch Affiliation
- School of Agricultural Sciences
- Resource Type
- Doctoral Thesis
UN Sustainable Development Goals (SDGs)
This output has contributed to the advancement of the following goals:
Metrics
50 File views/ downloads
83 Record Views