Gulls as reservoirs and vectors of high-risk, multidrug-resistant Escherichia coli in Atlantic Canada: emergence of CMY-2-producing ST648

Gulls ( Larus spp.) are key reservoirs and vectors of antimicrobial resistance (AMR). We characterized extended-spectrum β-lactamase (ESBL) and plasmid-mediated AmpC-producing Escherichia coli from Great Black-backed ( Larus marinus) and American Herring ( Larus smithsonianus) gulls in Nova Scotia, Canada. From 100 fecal samples collected from gulls visiting three fish-processing plants, 34 cefotaxime-resistant isolates were recovered: 29 ESBL and 5 AmpC producers. Detected β-lactamases included bla CTX-M-1 ( n = 12), bla CTX-M-55 ( n = 12), bla CTX-M-15 ( n = 2), bla CMY-2 ( n = 4), bla CTX-M-15 + bla TEM-1b ( n = 1), bla CTX-M-55 + bla TEM-1b ( n = 1), bla CTX-M-55 + bla TEM-1B + bla LAP-2 ( n = 1), and bla CMY-2 + bla TEM-1c ( n = 1). Additional resistance genes conferred resistance to sulfonamides ( sul2/ sul3), trimethoprim ( dfrA14/ dfrA17), tetracyclines ( tet( A)/ tet( B)), aminoglycosides, chloramphenicol ( floR), macrolides ( mph( A)), lincosamides ( lnu( F)), and quinolones ( qnrS), complemented by chromosomal mutations in gyrA, parC, and parE. The isolates represented phylogroups A ( n = 9), B1 ( n = 19), and D ( n = 6), and high-risk sequence types including ST155 ( n = 12), ST744 ( n = 7), ST224 ( n = 4), and ST648 ( n = 3). Plasmid analysis revealed a high replicon burden (≥3 in 70.6% of isolates), primarily IncFIB (70.6%), Col (58.8%), and IncI (50.0%). Key virulence factors detected were fimH (97.1%), lpfA (73.5%), fyuA (47.1%), and iss (38.2%). These results demonstrate that synanthropic gulls in Atlantic Canada carry multidrug-resistant ESBL/AmpC E. coli from globally significant clones, underscoring the role of these birds in dissemination of antimicrobial resistance within a One Health context.