Faecal pollution as potential driver of antibiotic resistance genes in the Danube River

Abstract

Human-induced antimicrobial resistance is an emerging concern in aquatic environments. Faecal pollution sources represent potential propagation pathways, however large-scale quantitative studies in whole river systems are missing. In the course of the Joint Danube Survey, the Danube River was investigated for the fourth time in summer 2019 from its headwaters to the delta. Microbial-faecal pollution patterns and the occurrence of selected antibiotic resistance genes (ARGs) were studied. Subsequently, a one-year time series analysis at selected relevant sites allowed to assess temporal variability. The intestinal bacterium Escherichia coli was quantified according to standard cultivation methods as indicator for total faecal pollution. In general, longitudinal patterns of faecal pollution showed a comparable picture to previous Joint Danube Surveys, with low to moderate pollution in the upper reaches (Germany, Austria) and critical to strong pollution in the middle and lower sections, especially in Serbia. Genetic microbial source tracking methods, determined via quantitative PCR, allowed us to define human faecal pollution as dominant pollution source along the whole Danube. This trend could be generally confirmed during the annual sampling campaign. To estimate the potential of permanent colonialization of faecal microorganisms within the Danube River ecosystem, biofilms as potential reservoirs were studied along the course of the entire river. Here, E.coli were ubiquitously present but highly variable. Ongoing analyses on the occurrence and quantity of selected ARGs will identify hotspots of antimicrobial resistance and their relationship to faecal pollution along the Danube River and thereby contribute to guide future monitoring and management strategies.