Patterns of Antibiotic Resistance Vary Widely Among Rivers

Spread of antibiotic resistance in different river systems compared for the first time. Harmonized study design of the Karl Landsteiner University of Health Sciences and ICC Water & Health lays the foundation.

Krems (Austria), 19 March, 2025: A new study provides important insights into the spread of antibiotic resistance (ABR) in different river systems. The study, conducted by researchers from the Karl Landsteiner University of Health Sciences (KL Krems) and partner organizations, uses a comprehensive, harmonized methodology that has been applied for the first time to compare different rivers. By analysing samples from four Lower Austrian rivers at different times of the year, it was possible to compare resistance trends with unprecedented statistical certainty. At the same time, a baseline for ABR pollution in Lower Austrian rivers was established for the first time. The results show that human faecal pollution is a critical factor in the spread of resistance genes in the aquatic environment. However, the nature and extent of this pollution varies greatly between rivers, despite the generally low levels of pollution in the rivers studied. This highlights the need for targeted monitoring, for which the work of KL Krems now provides an effective methodological basis.

Surface waters play a crucial role in the spread of antibiotic resistance (ABR). Sewage treatment plants, agricultural run-off and other sources of pollution contribute significantly to the emergence of antibiotic-resistant bacteria. Despite growing awareness, previous studies have used different methodologies and have mostly focused on individual water systems. This makes it impossible to compare them. Researchers at KL Krems have now developed a harmonized and cross-river study design that allows data from different rivers to be compared.

Individual Rivers

„Our research clearly shows that the distribution of ABR in rivers varies greatly,“ says Prof. Alexander Kirschner, microbiologist at MedUni Vienna, Karl Landsteiner University Krems and Deputy Head of ICC Water & Health*. „This discovery was only possible because we applied a comprehensive, harmonized methodology that allows us to compare the patterns of ABR in flowing waters. In particular, we took into account the role of the water itself and of biofilms“. In fact, the comparison has now shown for the first time that while pollution from human faeces generally has a strong influence, factors such as heavy metals, antibiotics, and river dynamics also correlate with ABR to varying degrees. Although possible causal relationships were not initially investigated.

This observation was based on data from four Austrian rivers (Danube, Kamp, Ybbs, Gölsen/Traisen) at five time points in one year. This spatial and temporal spread ensured that the interpretation of general ABR patterns was not biased by seasonal or site-specific characteristics. An extremely robust study design made the data comparable. More than 5,000 bacterial isolates were tested, over 100,000 ABR tests and more than 3,000 resistance gene analyses were performed. By combining classical cultivation techniques for the bacterium Escherichia coli (a clinically highly relevant indicator of ABR and faecal contamination) with quantitative analysis of resistance genes in the river microbiome, a uniquely detailed insight was gained. Combined with „smart“ genetic faecal diagnostics, it was also possible to differentiate between human and/or agricultural sources as the cause of ABR inputs.

Volume Matters

The details showed that human faecal pollution is an important factor in the spread of ABR, especially in small, low-flow rivers. In these low-flow river systems, factors such as heavy metal contamination and antibiotic residues were also more strongly correlated than in the Danube. In an international comparison, however, the four Austrian rivers showed low to moderate ABR contamination, indicating comparatively good wastewater management and high antibiotic stewardship standards in the country.

Biofilms – Hotspots or Cold Cases?

Biofilms – slimy communities of microorganisms on the surfaces of rocks, which have been described as hotspots of ABR in some small-scale studies – showed very inconsistent patterns of ABR spread in this study, depending on the specific local situation. In general, however, the correlation with pollution parameters was rather weak compared to water.

„Our work shows that specific statements about individual resistances or resistance genes are problematic,“ says Prof. Andreas Farnleitner, head of the ICC at KL Krems and TU Vienna. „Trends vary from stream to stream, and small studies carry the risk of over-interpretation. By combining different methods, we have now created a powerful framework for more precise, large-scale comparisons. What’s more, this is timely, as an EU regulation that will come into force in 2027 will require the monitoring of ABR in large wastewater treatment plants. The research conducted by KL Krems and ICC Water & Health together with the Medical Universities of Vienna and Graz and the University of Natural Resources and Applied Life Sciences Vienna at IFA Tulln thus provides policy makers and environmental authorities with the tools they need to respond effectively to current environmental challenges.

Original publication: Using a harmonised study design and quantitative tool-box reveals major inconsistencies when investigating the main drivers of water and biofilm antibiotic resistomes in different rivers. M. Leopold, C. Kolm, R. B. Linke, I. Schachner-Groehs, M. Koller, W. Kandler, C. Kittinger, G. Zarfel, A. H. Farnleitner & A. K.T. Kirschner. Journal of Hazardous Materials 488 (2025) 137343. DOI: 10.1016/j.jhazmat.2025.137343. https://kris.kl.ac.at/de/publications/using-a-harmonised-study-design-and-quantitative-toolbox-reveals-

Karl Landsteiner University of Health Sciences (03/2025)

The Karl Landsteiner University of Health Sciences (KL Krems) is an educational and research institution on the Campus Krems and recognised throughout Europe. KL Krems offers modern, demand-oriented education and continuing education in medicine and psychology as well as a PhD programme in Mental Health and Neuroscience. The flexible educational programme is tailored to the needs of students, the requirements of the labour market and the challenges of science. The three university hospitals in Krems, St. Pölten and Tulln and the MedAustron Ion Therapy and Research Centre in Wiener Neustadt guarantee clinical teaching and research of the highest quality. In its research, KL Krems focuses on interdisciplinary fields with high relevance to health policy – including biomechanics, molecular oncology, mental health and neuroscience as well as the topic of water quality and the associated health aspects. KL Krems was founded in 2013 and accredited by the Austrian Agency for Quality Assurance and Accreditation (AQ Austria).

https://www.kl.ac.at/en

*The ICC Water & Health is a cooperation between TU Wien, Medical University of Vienna and Karl Landsteiner University of Health Sciences (www.waterandhealth.at). The Inter-University Cooperation Center for Water and Health (ICC Water & Health) sees itself as a scientific platform and competent partner in questions of water quality and its impact on human health. The ICC is dedicated to the development of innovative concepts for assessing water quality, new microbiological and molecular biology methods, efficacy testing of physical and chemical treatment methods, and numerical models for estimating the risk of infection and disease in water use. The lessons learned will be used to derive effective and sustainable health management measures. The ICC was founded by the Vienna University of Technology and the Medical University of Vienna in 2010 and has been sustainably established thanks to the competitive research funding of the Federal Ministry of Science, Research and Economy (BMWFW). In 2017, ICC Water & Health was expanded to include the Karl Landsteiner University of Health Sciences (KL). KL is now an official part of the research platform.

www.waterandhealth.at

Scientific Contact

Prof. Andreas Farnleitner

Prof. Alexander Kirschner

Division Water Quality and Health

Karl Landsteiner University of Health Sciences

Dr.-Karl-Dorrek-Straße 30

3500 Krems an der Donau / Austria

T +43 664 605 88 22 44

+43 2732 72090 394

E andreas.farnleitner@kl.ac.at

alexander.kirschner@kl.ac.at