| Summary: | Colistin has been used for the treatment of non-invasive gastrointestinal infections caused by avian pathogenic <i>E. coli</i> (APEC). The discovery of mobilised colistin resistance (mcr) in <i>E. coli</i> has instigated a One Health approach to minimise colistin use and the spread of resistance. The aim of this study was to compare colistin susceptibility of APECs (collected from Denmark <i>n</i> = 25 and France <i>n</i> = 39) versus commensal <i>E. coli</i> (collected from the Netherlands <i>n</i> = 51 and the UK <i>n</i> = 60), alongside genetic (<i>mcr</i>-1–5) and phenotypic resistance against six other antimicrobial classes (aminoglycosides, cephalosporins, fluoroquinolones, penicillins, sulphonamides/trimethoprim, tetracyclines). Minimum inhibitory concentration (MIC) values were determined using a broth microdilution method (EUCAST guidelines), and phenotypic resistance was determined using disk diffusion. Colistin MIC values of APEC were significantly lower than those for commensals by 1 dilution (<i>p</i> < 0.0001, Anderson-Darling test), and differences in distributions were observed between countries. No isolate carried <i>mcr</i>-1–5. Three phenotypically resistant isolates were identified in 2/62 APEC and 1/111 commensal isolates. Gentamicin or gentamicin–ceftriaxone co-resistance was observed in two of these isolates. This study showed a low prevalence of phenotypic colistin resistance, with no apparent difference in colistin resistance between commensal <i>E. coli</i> strains and APEC strains.
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