Multidrug-resistant high-risk clonal *Escherichia coli* lineages occur along an antibiotic residue gradient in the Baltic Sea

The global spread of multidrug-resistant Escherichia coli threatens human, animal, and environmental health. Despite recognition of water bodies as reservoirs, research on AMR and antibiotic residues in the Baltic Sea is limited. This study examined ESBL-producing E. coli in surface water in northeastern Germany. Phenotypic and genotypic analyses encompassed AMR and heavy metal/metalloid tolerance, biofilm formation, and detailed plasmid examination. Solid-phase extraction with UHPLC–MS/MS quantified antibiotic residues. Thirty ESBL-producing E. coli isolates were identified, some associated with clinically relevant high-risk clonal lineages. Antibiotic residues were detected in environmental samples at significantly lower concentrations than in wastewater. The Baltic Sea surface water could serve as a reservoir for ESBL-producing E. coli and clinically relevant antibiotics.

Phillip Lübcke, Stefan E. Heiden, Timo Homeier-Bachmann, Jürgen A. Bohnert, Christian Schulze, Elias Eger, Michael Schwabe, Sebastian Guenther, Katharina Schaufler