Distinct ESBL dissemination mechanism associated with the hybrid transposon Tn/Tnin-carryingEnteritidis from poultry in South Korea.

Abstract

UNLABELLED: Extended-spectrum beta-lactamase (ESBL)-producingserovar Enteritidis (. Enteritidis) is emerging as a significant threat to food safety via its limitation of therapeutic options and potential transmission through poultry products. However, the structural and genetic characteristics of mobile genetic elements (MGEs) associated with horizontal transfer of the ESBL gene in. Enteritidis isolates from poultry remain insufficiently characterized. The present study aimed to identify and characterize the ESBL gene and its associated MGEs and to assess their distribution. Whole-genome sequencing was applied to ESBL-producing and non-ESBL-producing isolates in combination with pan-genome analysis, conjugation assays, and comparative genomics using publicly available genomes. Among 17 isolates, 9 were ESBL-producing and all carried. We observed co-transfer of,, and the IncF plasmid at relatively high frequencies (2.0-5.3 × 10⁻²) in ESBL-producing isolates. Moreover, we identified a hybrid transposon (Tn/Tn) inserted into IncF plasmids that comprised elements of Tn(,, and) and Tn(,, a DMT-family efflux gene, and a partial), with ISandadjacent to the hybrid transposon. Tn/Tnwas prevalent among-carrying. Enteritidis isolates from South Korea (19/20) but absent in those from other countries (= 9), suggesting geographical variation. This study identified a unique hybrid Tn/Tntransposon as the dominant MGE in-carrying. Enteritidis from South Korean poultry, highlighting its potential role in the regional dissemination of antimicrobial resistance. Continued surveillance and targeted intervention in poultry production are warranted to mitigate the spread of ESBL-producing. Enteritidis. IMPORTANCE: Extended-spectrum beta-lactamase (ESBL)-producingserovar Enteritidis from poultry represents a growing public health threat due to limited treatment options and the potential for transmission through the food chain. Despite this concern, the mobile genetic elements underlying ESBL gene dissemination remain insufficiently characterized in South Korean poultry-associated. Enteritidis isolates. In this study, we identified a hybrid transposon, Tn/Tn, embedded within IncF plasmids and linked toin. Enteritidis isolates. This association between Tn/Tnandsuggests a region-specific mechanism of resistance dissemination that may reflect antimicrobial selective pressure within poultry production systems. These findings highlight the importance of integrated One Health surveillance to mitigate the emergence and spread of antimicrobial resistance across animal and human populations.