Prevalence, antimicrobial resistance, and genetic characterization of Listeria monocytogenes in the Korean pork production chain.

Listeria monocytogenes, a major foodborne pathogen, causes invasive listeriosis with a high mortality rate. Its distribution and genomic diversity in livestock products in Korea remain poorly understood. This study investigated the prevalence and genomic characteristics of L. monocytogenes across Korean pork production and distribution chains. Samples from pigs, carcasses, meat, and the environment were collected from farms, slaughterhouses, and supermarkets nationwide. L. monocytogenes was recovered from 60 retail meat samples (19.0 %) but not from farms or slaughterhouses, suggesting that contamination occurs mainly during downstream processing and distribution. Whole-genome sequencing identified nine sequence types (STs) across two lineages, with Lineage II-ST9 being most prevalent. Within ST9, the core genome multilocus sequence typing-defined CT4379 subgroup was widespread across all provinces and harbored repUS43 plasmid replicon and tetM within a horizontal gene-transfer structure, also found in other Listeria STs and bacterial species. All ST9 isolates carried a premature stop codon (PMSC) in inlA. Two Lineage I-ST224 isolates were evolutionary linked to the outbreak strain FSCNU0110 in Korea in 2018, sharing an identical llsX PMSC in Listeria pathogenicity island (LIPI)-3. LIPI-4 was exclusively detected in ST87, a hypervirulent clone found in multiple provinces. Seven isolates from imported pork were ST3 and ST321, indicating potential international transmission via pork trade. All isolates possessed intrinsic antimicrobial resistance genes. The detection of persistent and hypervirulent clones in final pork products underscores the need for high-resolution genomic surveillance and strict hygiene interventions during meat processing and distribution for reducing the occurrence of listeriosis.