Abstract
We aimed to identify and characterize extended-spectrum β-lactamase (ESBL)-and/or plasmid-mediated AmpC β-lactamase (pAmpC)-producing Escherichia coli isolated from healthy broiler chickens slaughtered for human consumption in Korea. A total of 332 E. coli isolates were identified from 339 cloacal swabs in 2019. More than 90% of the isolates were resistant to multiple antimicrobials. ESBL/pAmpC-production was noted in 14% (46/332) of the isolates. Six of the CTX-M-β-lactamase-producing isolates were found to co-harbor at least one plasmid-mediated quinolone resistance gene. We observed the co-existence of blaCMY-2 and mcr-1 genes in the same isolate for the first time in Korea. Phylogenetic analysis demonstrated that the majority of blaCMY-2-carrying isolates belonged to subgroup D. Conjugation confirmed the transferability of blaCTX-M and blaCMY-2 genes, as well as non-β-lactam resistance traits from 60.9% (28/46) of the ESBL/pAmpC-producing isolates to a recipient E. coli J53. The ISECP, IS903, and orf477 elements were detected in the upstream or downstream regions. The blaCTX-M and blaCMY-2 genes mainly belonged to the IncI1, IncHI2, and/or IncFII plasmids. Additionally, the majority of ESBL/pAmpC-producing isolates exhibited heterogeneous PFGE profiles. This study showed that healthy chickens act as reservoirs of ESBL/pAmpC-producing E. coli that can potentially be transmitted to humans.
Highlights
Escherichia coli is a commensal bacterium of the intestinal tract of humans and animals
We identified 332 E. coli isolates from 339 fecal samples obtained from 34 different broiler farms
Our observations revealed that most of E. coli isolated from healthy broilers were resistant to multiple antimicrobials and possessed diverse ESBL-encoding genes that could be readily spread to humans
Summary
Escherichia coli is a commensal bacterium of the intestinal tract of humans and animals. It constitutes a reservoir of resistance genes for a wide range of pathogenic bacteria. The level of resistance in this bacterium is a good indicator of the selection pressure exerted by antimicrobial use and for the resistance problem to be expected in related pathogenic bacteria [1]. Healthy food animals are frequently reported as reservoirs of extended-spectrum β-lactamase (ESBL) and plasmid-mediated AmpC β-lactamase (pAmpC)-producing E. coli, and have caught considerable attention worldwide [3,4]. The ESBL/pAmpC enzymes are known to hydrolyze the β-lactam ring of β-lactam antibiotics and cause the emergence of resistance to a considerable number of β-lactam antibiotics, including extended-spectrum cephalosporins [5]. Human infections presumably occur following the ingestion of contaminated food of animal origin or via close contact with infected animals [7]
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