Serotype distribution, genotype, and antimicrobial resistance profiles of Salmonella enterica isolated from retail chicken meat in South Korea

Salmonella is a leading cause of foodborne illnesses worldwide, with poultry serving as the primary reservoir of this pathogen. Contaminated poultry meat products and eggs are major sources of human salmonellosis. In this study, 85 Salmonella isolates were collected from 120 retail chicken meat products in Korea and their serotype distributions, genetic characteristics, and antimicrobial resistance (AMR) profiles were analyzed. We identified 59 isolates (69.4%) as (i) Salmonella Infantis, (ii) belonging to sequence type (ST) 32 or its single-locus variant, and (iii) possessing the plasmid of the emerging S. Infantis (pESI)-like megaplasmid carrying the bla_CTX-M-65 gene. Among the 26 non-Infantis Salmonella isolates, only eight were serotyped as S. Enteritidis, S. Montevideo, and S. Typhimurium, whereas 18 untypeable isolates were clustered into six STs. Notably, high levels of resistance to three or more antibiotic classes, including β-lactams, aminoglycosides, phenicol, sulfonamide, tetracycline, and quinolone, were observed among the S. Infantis isolates. Additionally, mutations in the quinolone resistance-determining region (QRDR) of gyrA were identified in fluoroquinolone-resistant Salmonella isolates. Collectively, these findings suggest that multidrug-resistant ST32 S. Infantis is widely disseminated among retail chickens in Korea. The emergence of pESI-like megaplasmid and the increased levels of multidrug resistance in S. Infantis poses a significant threat to public health. Consequently, continuous surveillance of AMR profiles and the underlying mechanisms in Salmonella is crucial.