From In to Out: assessing antimicrobial-resistant Escherichia coli across treatment stages of wastewater

Authors

  • Tiago Merêncio Department of Biology, Faculty of Sciences of the University of Porto, Porto, Portugal
  • Ofélia Godinho CIMAR/CIIMAR– Interdisciplinary Centre for Marine and Environmental Research, University of Porto, Porto, Portugal
  • Olga Lage Department of Biology, Faculty of Sciences of the University of Porto, Porto, Portugal; CIMAR/CIIMAR– Interdisciplinary Centre for Marine and Environmental Research, University of Porto, Porto, Portugal
  • Sandra Quinteira Department of Biology, Faculty of Sciences of the University of Porto, Porto, Portugal; CIBIO—Research Center in Biodiversity and Genetic Resources, InBIO, Research Network in Biodiversity and Evolutionary Biology, Associated Laboratory, University of Porto, Campus de Vairão, Rua Padre Armando Quintas 7,4485-661 Vairão, Portugal; BIOPOLIS Program in Genomics, Biodiversity and Land Planning, Campus de Vairão, Rua Padre Armando Quintas 7, 4485-661 Vairão, Portugal; UCIBIO - Applied Molecular Biosciences Unit, Toxicologic Pathology Research Laboratory, University Institute of Health Sciences (1H-TOXRUN, IUCS-CESPU), 4585-116 Gandra, Portugal; Associate Laboratory i4HB - Institute for Health and Bioeconomy, University Institute of Health Sciences - CESPU, 4585-116 Gandra, Portugal

DOI:

https://doi.org/10.48797/sl.2025.339

Keywords:

Poster

Abstract

Background: Wastewater treatment plants (WWTPs) are critical points for the selection and transmission of antimicrobial resistance (AMR), which has become a major global public health concern [1,2]. The One Health approach is essential in addressing this issue, as AMR affects both human and environmental health [3]. Objective: To evaluate the role of WWTPs as reservoirs and/or sources of antimicrobial-resistant Escherichia coli, a key indicator of fecal contamination. Methods: Samples were collected from a WWTP located in northern Portugal, designed primarily for domestic sewage treatment. The sampling covered various stages of the treatment process: influent (untreated water), effluent (treated water), biological sludge, and dehydrated sludge, across four seasons (Spring, Summer, Autumn, and Winter). Escherichia coli levels were quantified using MUG-EC microplates (with and without ciprofloxacin, 1 µg/mL) for influent and effluent samples. Bacterial isolation and enumeration were performed using Chromogenic Coliform Agar (CCA) for all sample types, with isolate identification via 16S rRNA analysis. Antimicrobial susceptibility testing (AST) was conducted using the disk diffusion method (CLSI/EUCAST). Results: E. coli levels showed a reduction by a factor of approximately 10¹ (Autumn and Winter) to 10² (Spring and Summer) between influent and effluent. The study with ciprofloxacin showed that the levels of resistant strains increased in Spring but decreased in the other 3 seasons. In general, the enumeration of E. coli using CCA correlated with the MUG-EC results. The 16S rRNA gene affiliation resulted in non-discriminatory results between Escherichia spp. and Shigellaspp., leading to difficult AST interpretation. Despite this, variable susceptibility to gentamicin, tetracycline, ciprofloxacin, and imipenem was observed. Of concern, bacteria released into the environment via effluent (discharged directly into water bodies) and dehydrated sludge (used in agriculture) exhibited higher AMR profiles, including multidrug resistance (MDR). Conclusions: This study demonstrates that WWTP treatment effectively reduces microbial load. However, the presence of antimicrobial-resistant bacteria in effluents and sludge, particularly with MDR profiles, raises concerns regarding environmental dissemination. Given the seasonal variability in AMR levels and the small sample size, further studies are needed to comprehensively assess AMR throughout WWTPs and its environmental impact.

References

1. Wang, Y. et al. Distribution, sources, and potential risks of antibiotic resistance genes in wastewater treatment plant: A review. Environmental Pollution 2022, 310, 119870, doi: 10.1016/j.envpol.2022.119870

2. Godinho, O. et al. Antibiotic-Resistant Bacteria across a Wastewater Treatment Plant. Applied Microbiology 2024, 4(1), 364-375, doi: 10.3390/applmicrobiol4010025.

3. Aslam, B. et al. Antibiotic Resistance: One Health One World Outlook. Frontiers in Cellular and Infection Microbiology 2021, 11, 771510, doi: 10.3389/fcimb.2021.771510

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Published

2025-05-27

How to Cite

Merêncio, T., Godinho, O., Lage, O., & Quinteira, S. (2025). From In to Out: assessing antimicrobial-resistant Escherichia coli across treatment stages of wastewater. Scientific Letters, 1(Sup 1). https://doi.org/10.48797/sl.2025.339

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