Multidrug-resistant high-risk clonal Escherichia coli lineages occur along an antibiotic residue gradient in the Baltic Sea  : [Preprint]

The global spread of multidrug-resistant Escherichia coli threatens human, animal, and environmental health. Despite the recognition of water bodies as potential reservoirs, research on AMR in the Baltic Sea is limited. In this study, we examined the presence of ESBL-producing E. coli in surface water in northeastern Germany. We then conducted phenotypic and genotypic analyses of the strains, which encompassed AMR and heavy metal/metalloid tolerance, biofilm formation, and detailed plasmid examination. In addition, we used solid-phase extraction with ultra-high performance liquid chromatography and mass spectrometry to quantify antibiotic residues. Our analysis identified 30 ESBL-producing E. coli isolates, some of which were associated with clinically relevant high-risk clonal lineages. We detected antibiotic residues in the environmental samples, but the antibiotic concentrations were significantly lower compared to the wastewater samples. These results highlight the Baltic Sea surface water as a potential reservoir for ESBL-producing E. coli and clinically relevant antibiotics.