Antimicrobial resistance in wastewater-impacted coastal waters: implications for environmental surveillance and public health.

Authors

Niamh Cahill, Aneta Kovarova, Zina Alfahl, Louise O'Connor, Dearbháile Morris

Published in

Microbiology (Reading, England). Volume 172. Issue 9.

Abstract

Antimicrobial resistance (AMR) is a global public health concern, and wastewater-impacted aquatic environments are recognized as reservoirs and dissemination pathways for antimicrobial-resistant bacteria (ARB) and genes (ARGs). However, harmonized environmental AMR surveillance frameworks that integrate culture-based ARB enumeration with molecular ARG monitoring across wastewater and receiving surface waters remain limited. This pilot study, conducted in Ireland as part of a European harmonized monitoring initiative, assessed ARB and ARG abundances in wastewaters and surface waters. Wastewater treatment plant influent (n=3), effluent (n=3) and surface waters upstream and downstream of the discharge point (n=3 each) were sampled on three occasions in late 2024. Culture-based methods enumerated total and extended-spectrum β-lactamase (ESBL)-producing Escherichia coli, while quantitative real-time PCR quantified 16S rRNA and five AMR-associated genes (intI1, ermB, aadA1, bla _CTX-M-1 and vanA). Total E. coli concentrations were highest in influent (~10⁵-10⁶ c.f.u. dl^-1), decreased in effluent (~10³-10⁵ c.f.u. dl^-1) and lowest in surface waters (~10¹-10² c.f.u. dl^-1). ESBL-producing E. coli were consistently detected in influent (~10⁴ c.f.u. dl^-1) and effluent (~10¹-10³ c.f.u. dl^-1) but were not recovered from seawater. ARG abundances were highest in influent, reaching up to ~10¹¹ copies dl^-1 for intl1, remained elevated in effluent (up to ~10¹⁰ copies dl^-1) and were ~2-3 orders of magnitude lower in surface waters relative to effluent. Downstream seawater exhibited higher ARG levels than upstream freshwater despite low culturable E. coli. Peak ARG concentrations in effluent and surface waters were observed following a period of heavy rainfall; however, the limited number of sampling events precluded assessment of any statistical association. These findings highlight the impact of wastewater discharges on environmental AMR dissemination and suggest that faecal indicator-based monitoring may underestimate emerging risks, supporting integration of AMR indicators into EU water quality frameworks.

PMID:
42704659
Bibliographic data and abstract were imported from PubMed on 08 Sep 2026.

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