Transferable IncX3-blaKPC-2 plasmid and chromosomal blaCTX−M-27 in a commensal Escherichia coli ST7854 isolated from a healthy companion dog

Abstract

Objectives

Carbapenemase-producing Enterobacterales have disseminated globally, largely via highly transmissible plasmids. Their emergence in companion animals is of particular concern, indicating that clinically important carbapenem-resistance determinants have spread beyond healthcare settings. This study characterized a multidrug-resistant Escherichia coli isolate from a healthy dog in South Korea.

Methods

Antimicrobial susceptibility was determined by standardized reference methods. Hybrid whole-genome assembly resolved chromosomal and plasmid architectures, and plasmid transferability was assessed by conjugation assays. Comparative genomic analysis based on nucleotide identity and alignment coverage evaluated relatedness to publicly available bla_KPC-carrying IncX3 plasmids.

Results

The E. coli ST7854 isolate was resistant to carbapenems (imipenem MIC = 8 µg/mL), third-generation cephalosporins, fluoroquinolones, tetracycline, gentamicin, phenicols, and trimethoprim–sulfamethoxazole, but susceptible to amikacin and colistin. Assembly resolved a 4.77 Mb circular chromosome and seven plasmids. The ESBL gene bla_CTX−M-27 was chromosomally integrated, whereas carbapenem resistance was conferred by bla_KPC-2 on a 54,805 bp IncX3 plasmid. This IncX3-bla_KPC-2 plasmid was transferred to E. coli J53 at a frequency of 5.91 × 10⁻⁴, whereas the large IncFIB multidrug resistance plasmid was not co-transferred. Comparative analysis revealed extensive structural similarity with Korean clinical IncX3 plasmids, whereas most representative international plasmids shared only the conserved IncX3 backbone.

Conclusions

A commensal E. coli ST7854 isolate from a healthy companion dog carried a conjugative IncX3-bla_KPC-2 plasmid and chromosomally integrated bla_CTX−M-27. Similarity to Korean clinical plasmids suggests potential human–animal dissemination, and this asymptomatic carriage of mobile carbapenem-resistance determinants supports continued genomic surveillance of antimicrobial resistance in companion animals within a One Health framework.