Molecular Epidemiology and Genetic Context of -Carrying Linezolid-Resistant Enterococci from Humans and Animals in South Korea.

Linezolid resistance among species poses a growing clinical and public health concern, especially due to the dissemination of transferable resistance genes, such as . This study aimed to evaluate the prevalence of linezolid resistance and to characterize the molecular epidemiology and genetic contexts of -positive linezolid-resistant (LRE) isolates from clinical and animal sources in South Korea. A total of 2156 isolates, collected through nationwide surveillance from hospitalized patients and healthy livestock (pigs, cattle, and chickens) between 2017 and 2019, were retrospectively analyzed. Phenotypic susceptibility testing, gene screening, and whole-genome sequencing were performed to investigate genetic environments and phylogenetic relationships. The prevalence of linezolid resistance was 0.2% in clinical isolates, 3.3% in pigs, 4.3% in cattle, and 1.4% in chickens. -positive linezolid-resistant isolates were less frequent, with rates of 0.1%, 1.4%, 0.9%, and 1.0%, respectively. Multilocus sequence typing identified sequence types (STs) 330 and ST476 in from humans, with no shared STs between human and livestock isolates. The gene was located either chromosomally, frequently associated with transposon Tn6674, or on multidrug resistance plasmids. Notably, variants exhibited host-specific distribution patterns. Phylogenetic analysis demonstrated considerable genomic diversity, and Korean ST476 isolates were genetically related to international strains reported from livestock, poultry products, and wild birds, suggesting potential global dissemination. This study provides a comprehensive, nationally representative assessment of linezolid resistance in South Korea. The findings highlight the zoonotic potential and possible international dissemination of -carrying ST476 lineages, underscoring the need for integrated One Health surveillance to monitor and control the spread of transferable resistance genes.