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Gulls at Nova Scotia Fish Plants Carried High-Risk Multidrug-Resistant E. coli

Great black-backed gull at Signal Hill in St. John's, Newfoundland
Research: Disease, parasites & microbiology, Genetics & genomics

Great black-backed gulls (Larus marinus) and American herring gulls (Larus smithsonianus) visiting three fish-processing plants in Nova Scotia, Canada were carrying antibiotic-resistant Escherichia coli, according to a 2026 study. E. coli is a common gut bacterium in animals and people, although some lineages can cause disease. The concern here was not that the gulls were necessarily ill, but that bacteria in their intestines carried resistance that can make important antibiotics less effective.

Researchers collected 100 gull faecal samples and recovered 34 E. coli isolates resistant to cefotaxime, a third-generation cephalosporin used against serious bacterial infections. Detecting the bacteria in faeces shows that gulls were carrying and shedding them at the sampling sites; it does not by itself show where the bacteria were acquired or that they were transmitted to people, fish or other animals.

Most resistant isolates produced enzymes that disable cephalosporins

Twenty-nine of the 34 isolates produced extended-spectrum beta-lactamases (ESBLs), while five produced plasmid-mediated AmpC beta-lactamases. These are bacterial enzymes that can break down beta-lactam antibiotics; ESBL and AmpC mechanisms are particularly important because they can undermine newer cephalosporins such as cefotaxime. The main resistance genes included blaCTX-M-1, blaCTX-M-55 and blaCMY-2.

Many isolates also carried genes associated with resistance to other antimicrobial groups, including tetracyclines, sulfonamides, trimethoprim, aminoglycosides and quinolones. The result therefore reflects resistance to multiple drug classes rather than resistance to a single antibiotic.

Several bacterial lineages are already distributed internationally

Genomic typing showed that the resistant bacteria belonged to several sequence types, including ST155 in 12 isolates, ST744 in seven, ST224 in four and ST648 in three. A sequence type is a genetic lineage identified from a standard set of bacterial markers. These particular lineages have been reported internationally in people, animals and environmental samples, which is why the authors describe them as high-risk clones.

Plasmids provide another route by which resistance can spread. These small, usually circular DNA molecules can move between bacteria and often carry resistance genes with them. At least three plasmid types were detected in 70.6% of the isolates, showing that many of the gull-associated bacteria carried several potential vehicles for mobile resistance genes. This does not prove that gene transfer occurred in the gulls themselves, but it shows that the genetic machinery capable of moving resistance was common in the sampled bacteria.

The finding links wildlife to a wider One Health problem

The authors interpret the results within a One Health framework, which considers human, animal and environmental health together. Gulls regularly move between natural areas and human food- and waste-rich environments, so resistant gut bacteria they carry can potentially be transported between locations. The Nova Scotia study therefore identifies gulls as possible reservoirs and dispersers of antimicrobial resistance, while stopping short of demonstrating a specific transmission route from gulls to humans or other animals.

Sources and image credit

  1. Ben Sallem, R., Bouallegue, O., Quinlan, T., Theriault, M., Kaouass, M., Craik, S., & Wong, A. (2026). Gulls as reservoirs and vectors of high-risk, multidrug-resistant Escherichia coli in Atlantic Canada: Emergence of CMY-2-producing ST648. Canadian Journal of Microbiology, 72, 1–14. https://doi.org/10.1139/cjm-2025-0240Primary research article. One hundred faecal samples were collected from Great Black-backed and American Herring Gulls visiting three fish-processing plants in Nova Scotia. Thirty-four cefotaxime-resistant E. coli isolates were recovered, including 29 ESBL and five AmpC producers; high-risk sequence types included ST155, ST744, ST224 and ST648.

Image: Ryan Hodnett / Wikimedia Commons. Great black-backed gull at Signal Hill, St. John’s, Newfoundland, 22 August 2019; illustrative species photograph, not from the Nova Scotia sampling sites. · CC BY-SA 4.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

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