Recent Occurrence and Rapid Spread of Multidrug-ResistantInfantis in Broiler Flocks in Korea.

Abstract

Infantis has recently been one of the most prevalent serotypes in poultry and has been identified in human salmonellosis cases worldwide. Multidrug-resistant (MDR)Infantis has emerged as a significant threat to both poultry production and public health due to its increasing prevalence and global dissemination. We identified the occurrence of an MDRInfantis clone in broiler flocks in Korea, and the clone was characterized to explore potential genetic causes for its high prevalence and rapid spread in broiler production. In total, 220strains isolated between 2020 and 2023 from broiler flocks were serotyped, and 50 strains were identified asInfantis (22.7%). The isolates were tested for antimicrobial susceptibility, and their genetic characteristics were analyzed using pulsed-field gel electrophoresis (PFGE), multilocus sequence typing, and whole genome sequencing (WGS). Forty-six strains ofInfantis isolated since 2020 were resistant to at least five antimicrobial families including ampicillin, cephalosporins, chloramphenicol, nalidixic acid, and tetracycline. The strains showed 10 PFGE patterns and a single multilocus sequence type 32. Eight representative MDR strains were analyzed by WGS. Seven of the eight strains carried the plasmid of emergingInfantis-like megaplasmids recognized globally in emergent MDRInfantis. They had a high prevalence of seven antimicrobial resistance genes, six of which were identified in plasmids. Also, they all share virulence genes, including fimbrial adherence determinants and secretion system components, and showed a clonal relationship to strains from North America, South America, and West Asia, suggesting potential international dissemination routes. To mitigate the risks associated with the rapid spread of MDRInfantis in poultry production and its potential impact on human health, this study provides valuable insights into implementing effective control measures to reducein broiler production in Korea. Further highlighting the critical importance of enhanced biosecurity and continuous surveillance.