How does antibiotic resistance affect Lower Austria's rivers?

Antibiotic resistance in rivers and wastewater is increasingly attracting scientific and public interest. In order to obtain the first comprehensive data on the occurrence of such resistance in Lower Austrian rivers, water samples from four rivers were analysed. The samples came from different sections - from clean headwaters to areas downstream of sewage treatment plants, whose catchment areas also contained wastewater from hospitals. "The investigations focussed on a section of the Danube near Krems and Traismauer, where two municipal sewage treatment plants discharge, as well as three tributary rivers: the Ybbs, the Traisen and the Kamp. The study analysed whether these waters are polluted by discharges from wastewater treatment plants with clinical wastewater - for example from hospitals in Zwettl, Amstetten, Krems and St. Pölten. For comparison, so-called reference sites were also included, for example upstream of Lunz or near Herzogenburg, where there is no or only minimal influence from wastewater treatment plants. These sites serve as a baseline for assessing the pollution," explains Prof. Dr. Alexander Kirschner, Deputy Head of the Department.

The study pursued two central questions: Firstly, the health-relevant burden of resistant bacteria was investigated, and secondly, how the corresponding resistance genes have already spread in the bacterial communities of the rivers. "We analysed Escherichia coli as a model pathogen with high relevance for humans. This indicator is also recommended by the WHO for environmental monitoring. A total of 2,736 isolates were obtained and tested for their resistance to 20 different antibiotics - a very extensive data set that was collected by our doctoral student Melanie Leopold with the support of students," explains the expert. In addition, nine different antibiotic resistance genes were analysed, including those of high clinical relevance that occur only rarely and often play a role in reserve antibiotics. "We analysed how these genes have spread in the microbiomes of rivers - especially after discharge points from sewage treatment plants," says Prof. Dr. Andreas Farnleitner, co-head of the study and head of the department.

Results and international classification
Four measuring points were selected on each river, each of which was sampled five times over the course of a year (October to October). This also allowed the temporal development to be assessed - for example, whether seasonal fluctuations play a role. "Overall, Austria has very good wastewater treatment, which is primarily aimed at removing nutrients such as carbon, nitrogen and phosphorus compounds. The reduction of pathogenic germs is a very positive side effect. Nevertheless, pathogens, faecal bacteria and resistance genes continue to enter the environment despite the purification stages," says Alexander Kirschner, describing the results. An international comparison of the emission of resistance and resistance genes shows that Austria has a low level of contamination within Europe, similar to the Scandinavian countries. The concentrations measured in the river sections analysed therefore do not currently give any immediate cause for concern. At the same time, the data situation is still inadequate in many areas. In particular, the long-term persistence of resistant bacteria and resistance genes, their effects on humans, animals and the environment and the link to agricultural sources have hardly been researched to date.

One Health approach and further measures 
The results also emphasise the importance of the One Health approach, which views humans, animals and the environment as an interconnected system. "On the one hand - as is currently being discussed and proposed under the new EU Wastewater Directive - the expansion of municipal wastewater treatment plants to include a future fourth treatment stage to reduce chemical trace substances would be of great benefit. This could also contribute to the further removal of antibiotic resistance. However, the continued restrained use of antibiotics, particularly in clinical and general practice settings, is just as important as further monitoring in future studies in order to recognise changes at an early stage and evaluate developments." The conclusion: "The study makes an important contribution to assessing the environmental impact of antibiotic resistance in Austrian waters. It shows that, despite favourable framework conditions, there is still a need for action - both in the investigation of future environmental emissions and in the responsible use of antibiotics," concludes Alexander Kirschner.

Link to the study: First comprehensive quantitative survey of antibiotic resistance in four Lower Austrian rivers - Karl Landsteiner University of Health Sciences, Interuniversity Cooperation Centre Water&Health, www.waterandhealth.at

More about the research at KL Krems: https://www.kl.ac.at/de/forschungsblog