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 blaCTX-M-1 (n = 12), blaCTX-M-55 (n = 12), blaCTX-M-15 (n = 2), blaCMY-2 (n = 4), blaCTX-M-15 + blaTEM-1b (n = 1), blaCTX-M-55 + blaTEM-1b (n = 1), blaCTX-M-55 + blaTEM-1B + blaLAP-2 (n = 1), 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 = 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.