Assessment of Escherichia coli as an indicator of antimicrobial resistance and monitoring of ESBL/AmpC-Producing Enterobacteriaceae in retail seafood commonly consumed in Italy.

This study assessed Escherichia coli as an indicator of antimicrobial resistance (AMR) in retail seafood, integrating microbiological and genomic analyses within a One Health perspective. Overall, E. coli was cultured from 55 (13%) of 422 raw samples from seven seafood categories commonly consumed in Italy. E. coli was detected across multiple seafood types, but particularly in bivalves (23%) and crustaceans (20%). Because these species can accumulate or acquire faecal contaminants from the aquatic environment or along the post-harvest chain, they represent relevant matrices for AMR monitoring. In parallel, we investigated the presence of Extended-β-Lactamase ESBL-, AmpC- and carbapenemase-producing Enterobacteriaceae. Cefotaxime-resistant E. coli isolates were identified at low but relevant frequencies, especially in bivalves, and were characterised phenotypically and by whole-genome sequencing. Most isolates carried clinically important ESBL or AmpC genes, more frequently blaCTX-M-15, often on contigs predicted as plasmid-associated, indicating their potential for horizontal spread. An ESBL-producing Atlantibacter hermannii harbouring blaCTX-M-55 was also recovered from frozen shrimps. Additional AmpC-producing Enterobacteriaceae, including Citrobacter and Enterobacter species, were detected in a subset of samples. Overall, our findings support the suitability of E. coli as an AMR indicator organism for retail bivalves and crustaceans. The detection of ESBL-producing strains, carrying important plasmid-borne resistance determinants, highlights the need to strengthen AMR surveillance in these seafood commodities.