Faecal pathways of antibiotic resistance along the entire length of the Danube

The increase in antibiotic resistance poses a global threat to human and animal health. In the EU alone, an estimated 25,000 patients die each year from hospital-acquired infections with antibiotic-resistant bacteria. Outside hospitals, antibiotic-resistant bacteria (ARB) and antibiotic resistance genes (ARG) are spreading in aquatic ecosystems, among other places. These affect humans and animals in the course of drinking water and livestock water extraction, irrigation or bathing, especially in large river systems with many inhabitants.

In this project, the Danube – the second longest river in Europe and the most international river in the world – will be studied along its entire length, including its most important tributaries, in order to determine the sources, pathways and factors that influence the presence and spread of ARB and ARG. A new holistic and quantitative concept has been developed to test the following hypotheses:

1. The faecal input into surface water correlates with changes in the resistant population. The concentration of ARB and ARG also depends on their persistence in the environment and the hydrological conditions.
2. In biofilms and fine sediments, the amounts of ARB and ARG are decoupled from the extent of faecal contamination. ARB and ARG accumulate depending on specific ecological selection factors and qualitative changes in faecal pollutant input (untreated/treated wastewater, different antibiotic usage patterns in different countries).
3. The distribution patterns of ARB and ARG can vary greatly between different bacterial species, and using only one species would lead to a distorted picture of the distribution of antibiotic resistance in water bodies.

The new concept is based on determining ARB and ARG concentrations in several bacterial model organisms, which are analysed in water and biofilm using a combination of cultivation and genetic methods. This data will be combined with quantitative information on the extent and sources of faecal pollution and a comprehensive assessment of environmental conditions as part of the Joint Danube Survey (JDS), the world's largest river research expedition.

To date, the distribution of ARB and ARG in water bodies has only been studied on a small scale, taking into account a relatively small number of environmental parameters. The proposed quantitative total river concept will, for the first time, provide a comprehensive picture of the main factors influencing the distribution of ARB and ARG along the entire length of a major river in an international context. This will stimulate new ideas for understanding and managing microbial water quality and antibiotic resistance in major rivers.