Constructed wetlands as nature-based barriers: Mitigating antimicrobial resistance and pathogen dispersal in riverine systems

Antimicrobial resistance (AMR) is an emerging global health crisis which necessitates a multidisciplinary strategy which recognise the interconnectedness of human, animal, and environmental health, embodies in the One Health approach. An increasing number of contaminants, including pathogens, antimicrobial resistant bacteria (ARB) and antimicrobial resistance gene (ARGs) are now classified as emerging pollutants affecting freshwater ecosystems. The discharge of these pollutants from wastewater treatment plans (WWTP), agricultural run-off, and industrial waste alters the microbial community in receiving water bodies and facilitate the environmental dispersal of AMR. This study investigates the contribution of an integrated constructed wetland (CW) in improving a WWTP effluent quality before release into a chalk stream, particularly focusing on the reduction of ARGs and ARB. The study involved four sampling campaigns conducted every two months to assess seasonal variations of the system on ARGs and ARB load. Results indicated that microbial communities within the CW varied spatially and seasonally, influencing ARG profiles. Despite similar overall ARG loads across sampling periods, significant shifts in microbial community composition were observed. Notably, the CW demonstrated the ability to reduce potentially pathogenic bacteria, including antibiotic-resistant E. coli strains resistant to last-resort antibiotics such as colistin and carbapenems. Particularly, colistin-resistant isolates were detected only in the first CW cell receiving the WWTP effluent, highlighting the system's potential to act as a nature-based barrier against AMR dissemination. Overall, these findings enhance our understanding of CW systems, offering valuable insights for optimizing management strategies. By improving performance and efficacy, this research contributes to the development of sustainable nature-based solutions for mitigating environmental pollution, protecting freshwater ecosystems and public health.