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Infantis), a major cause of human salmonellosis, is commonly associated with transmission via contaminated chicken meat. This study, as part of the national\n                      <jats:italic toggle=\"yes\">Salmonella<\/jats:italic>\n                      monitoring program, assessed the prevalence of\n                      <jats:italic toggle=\"yes\">S. enterica,<\/jats:italic>\n                      including\n                      <jats:italic toggle=\"yes\">S<\/jats:italic>\n                      . Infantis, in chicken slaughterhouses across South Korea from 2014\u20132022. The presence of a megaplasmid, known as plasmid of emerging\n                      <jats:italic toggle=\"yes\">S<\/jats:italic>\n                      . Infantis (pESI), was confirmed. This confirmation was based on multidrug-resistant and third-generation cephalosporin-resistant\n                      <jats:italic toggle=\"yes\">S<\/jats:italic>\n                      . Infantis isolates using whole-genome sequencing. Phenotypic and genotypic characterization involved antimicrobial susceptibility tests, pulsed-field gel electrophoresis, polymerase chain reaction to screen for pESI plasmids, plasmid profiling, and conjugation assays.\n                      <jats:italic toggle=\"yes\">S<\/jats:italic>\n                      . Infantis was identified in 9.3% of\n                      <jats:italic toggle=\"yes\">Salmonella<\/jats:italic>\n                      -positive samples in 2014, undetected from 2015\u20132020, but re-emerged as the predominant serovar in 2021 (54.7%) and 2022 (75.5%). The isolates in 2014 were antibiotic susceptible, whereas most isolates from 2021 to 2022 exhibited multidrug-resistance, including resistance to third-generation cephalosporins. All isolates were sequence type 32 (ST32), with core genome multilocus sequence typing demonstrating pESI plasmid-based clustering. The pESI\n                      <jats:sup>+<\/jats:sup>\n                      isolates harbored genes, such as\n                      <jats:italic toggle=\"yes\">aadA1<\/jats:italic>\n                      ,\n                      <jats:italic toggle=\"yes\">dfrA14<\/jats:italic>\n                      ,\n                      <jats:italic toggle=\"yes\">sul1<\/jats:italic>\n                      , and\n                      <jats:italic toggle=\"yes\">tetA<\/jats:italic>\n                      , and three multidrug-resistant pESI\n                      <jats:sup>+<\/jats:sup>\n                      isolates harbored\n                      <jats:italic toggle=\"yes\">\n                        bla\n                        <jats:sub>CTX-M-65<\/jats:sub>\n                      <\/jats:italic>\n                      . The plasmids were genetically similar to those observed in\n                      <jats:italic toggle=\"yes\">S<\/jats:italic>\n                      . Infantis from broilers, chicken meat, and human clinical samples across various countries. This study highlights the spread of multidrug-resistant\n                      <jats:italic toggle=\"yes\">S<\/jats:italic>\n                      . Infantis harboring the pESI plasmid with\n                      <jats:italic toggle=\"yes\">\n                        bla\n                        <jats:sub>CTX-M-65<\/jats:sub>\n                      <\/jats:italic>\n                      during early chicken production in South Korea. Continuous monitoring and control of resistant\n                      <jats:italic toggle=\"yes\">S<\/jats:italic>\n                      . Infantis throughout the food chain is essential to inform public health initiatives.\n                    <\/jats:p>\n                    <jats:sec>\n                      <jats:title>IMPORTANCE<\/jats:title>\n                      <jats:p>\n                        This study highlights the critical emergence of multidrug-resistant (MDR)\n                        <jats:italic toggle=\"yes\">Salmonella enterica<\/jats:italic>\n                        serovar Infantis (\n                        <jats:italic toggle=\"yes\">S<\/jats:italic>\n                        . Infantis) in South Korea\u2019s chicken slaughterhouses, driven by the acquisition of the pESI megaplasmid harboring the extended-spectrum beta-lactamase (ESBL) determinant\n                        <jats:italic toggle=\"yes\">\n                          bla\n                          <jats:sub>CTX-M-65<\/jats:sub>\n                        <\/jats:italic>\n                        . Using whole-genome sequencing and comprehensive phenotypic-genotypic analyses, the findings reveal that pESI\n                        <jats:sup>+<\/jats:sup>\n                        isolates in South Korea are genetically similar to strains from broilers, chicken meat, and human clinical cases worldwide. This underscores the transboundary nature of\n                        <jats:italic toggle=\"yes\">S<\/jats:italic>\n                        . Infantis and its potential as a global public health threat.\n                      <\/jats:p>\n                    <\/jats:sec>\n                  <\/jats:sec>","DOI":"10.1128\/spectrum.02955-24","type":"journal-article","created":{"date-parts":[[2025,6,2]],"date-time":"2025-06-02T09:34:52Z","timestamp":1748856892000},"update-policy":"https:\/\/doi.org\/10.1128\/asmj-crossmark-policy-page","source":"Crossref","is-referenced-by-count":14,"title":["Emergence and characteristics of multidrug-resistant\n                    <i>Salmonella enterica<\/i>\n                    subspecies\n                    <i>enterica<\/i>\n                    serovar Infantis harboring the pESI plasmid in chicken slaughterhouses in South 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