Löffler, Paul
- Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences
Antimicrobial chemicals, including antibiotics and antivirals, are essential medicines for human and animal health, but their effectiveness is increasingly threatened by the development of antimicrobial resistance (AMR). While the role of the environment in the emergence and dissemination of AMR is recognized, it remains insufficiently understood. Antibiotics are often excreted as metabolites, and additional residues can degrade in the environment. Collectively, these metabolites and degradation products are referred to as transformation products (TPs), whose environmental fate and biological activity have received limited attention.
This thesis advances the understanding of antimicrobial TPs in aquatic environments by combining literature reviews, global occurrence studies, computational assessments, chemical analysis, and microbiological experiments. A systematic literature review identified 56 distinct antimicrobial TPs reported in surface waters worldwide, while emphasizing major geographical knowledge gaps. Complementary sampling from six countries revealed 27 additional TPs. Photolysis experiments demonstrated that some TPs are highly stable under environmental conditions, while others degrade depending on water matrix composition. To support risk prioritization, existing computational tools were reviewed. A new workflow integrating pH-dependent ionizability was proposed and applied to prioritize the TPs identified in the literature study based on ecological and resistance risks. Molecular dynamics simulations suggested that several sulfonamide and trimethoprim TPs retain binding affinity to bacterial targets, and antibacterial activity of multiple macrolide, tetracycline, and lincosamide TPs was experimentally confirmed through minimum inhibitory concentration assays and microcosm studies.
Overall, this thesis demonstrates that antimicrobial TPs can persist in surface waters, retain biological activity, and can contribute to selection pressure on microbial communities. These findings underscore the need to include TPs in the assessment of AMR in the environment.
surface waters; environmental fate; antibiotic metabolites; resistance genes; environmental monitoring; degradation products; risk assessment
Acta Universitatis Agriculturae Sueciae
2025, number: 2025:82
Publisher: Swedish University of Agricultural Sciences
Environmental Sciences
Oceanography, Hydrology, Water Resources
https://res.slu.se/id/publ/142483