Antimicrobial resistance (AMR) in the wastewater-environment continuum: What a Wales national study revealed
Antimicrobial resistance (AMR) is not only a clinical issue, it moves through our environment, often unnoticed. In a study by Knight et al., conducted across Wales, researchers followed AMR genes from untreated wastewater through treatment plants and into rivers, estuaries, and beaches. By using high-throughput qPCR, they revealed how human activity contributes to AMR in nature and why understanding this flow is critical to public health and policy. Resistomap contributed by providing SmartChip qPCR analysis for quantifying ARGs and mobile genetic elements (MGEs) in this landmark study.
As described in the study, the team collected samples from 47 wastewater treatment plants (WWTPs), covering around 66% of the population connected to the sewer system. On average, 68 unique ARGs were detected in untreated wastewater, with resistance to macrolides, aminoglycosides, and fluoroquinolones being the most abundant. ARG abundance and composition were found to be associated with population size and density.
Following treatment, the number of ARGs dropped, but not completely. Treated effluent still carried an average of 57 resistance genes, with notable variation based on the treatment method used. Biological filter beds were more effective than activated sludge in reducing ARG levels, and UV disinfection had no significant effect on the resistome composition .
The study extended beyond treatment plants, sampling river and coastal sediments to evaluate downstream impacts. All environmental samples contained ARGs, with estuarine and beach sediments sometimes showing higher resistance gene abundance than the treated effluent itself .
However, ARG levels and diversity didn’t consistently rise downstream, suggesting that AMR in the environment is shaped by multiple sources, not just WWTPs. Agricultural runoff, urban pollution, and regional population size all possibly contribute to sediment resistome variation .
This large-scale, data-rich study highlights the importance of national surveillance in monitoring AMR across human and environmental health sectors. It also demonstrates the value of tools like qPCR and contributors like us at Resistomap, in generating actionable, quantitative insights to support One Health approaches to AMR mitigation.
Source: Knight M.E., Farkas K., Kiss A., Jones D.L. National-scale insights into AMR transmission along the wastewater-environment continuum. Water Research. 2025.
doi.org/10.1016/j.watres.2025.123603
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