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 AmpCproducing Escherichia coli from Great Black-backed (Larus marinus) and American Herring (Larus smithsonianus) gulls in Nova Scotia, Canada. From 100 fecal samples, 34 cefotaxime-resistant isolates were recovered: 29 ESBL and 5 AmpC producers. Detected, and blaCMY-2 + blaTEM-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=10), B1 (n=18), 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 their role in the dissemination of antimicrobial resistance within a One Health context.