Genetic analysis of pESI-like megaplasmid in Salmonella Infantis from the poultry industry in Korea.

The plasmid of emerging Salmonella Infantis (pESI) and pESI-like plasmids have been reported as a major cause of the dissemination of S. Infantis worldwide, and these plasmids have also been reported in Korea. In this study, eight pESI or pESI-like plasmids, including two pESI-like plasmids of S. Infantis from the poultry industry in Korea, harbored yersiniabactin operon, toxin/antitoxin systems, and fimbria clusters. Interestingly, various resistance genes were identified in the pESI-like plasmids but not in the pESI plasmid. In particular, dfrA14, which confers resistance to trimethoprim, was harbored in one copy in seven pESI or pESI-like plasmids, but the pM6-2-F5 plasmid harbored two copies. Additionally, the copy number of insertion sequence 26 in seven pESI-like plasmids was higher than in the pESI plasmid. In this study, 40 S. Infantis strains carrying the pESI or pESI-like plasmids from various countries, including two strains in Korea, were classified into two clusters, with the plasmids identified as IncI1 ST71 in cluster I and IncI1 ST209 in cluster II. The 16 strains representing IncI1 ST71 harbored blaCTX-M-65, whereas the 8 strains representing IncI1 ST209 harbored blaCTX-M-1. Our study provides valuable information on the pESI-like plasmid in S. Infantis from the poultry industry worldwide.