Multiple Introductions and Cross-Sector Transmission of Salmonella enterica Serovar Infantis Carrying blaCTX-M-65 Gene, South Korea, 2022-2024.

Salmonella enterica subspecies enterica serovar Infantis carrying the blaCTX-M-65 gene has been increasingly detected globally, including in South Korea, since 2022. We analyzed 65 blaCTX-M-65-positive Salmonella Infantis isolates from humans, poultry, and wastewater collected during 2022-2024 by using whole-genome sequencing and phylogenomic analysis. All isolates were multidrug resistant, commonly to aminoglycosides, β-lactams, quinolones, tetracyclines, amphenicols, and folate pathway inhibitors. Phylogenetic analysis revealed high genetic similarity among isolates from humans, poultry, and wastewater, which were intermingled within monophyletic clades with high bootstrap support, indicating close genomic relatedness across sectors. Bayesian phylogeographic reconstruction suggested multiple potential introductions during 2018-2022, including 1 lineage related to isolates from the United States (clade I) and others related to isolates from the United Kingdom (clade II). Those findings highlight the emergence and genomic diversity of blaCTX-M-65-positive Salmonella Infantis in South Korea and support the value of continued genomic surveillance across sectors.