Dissemination of IncI2 Plasmids That Harbor the bla_CTX-M Element among Clinical Salmonella Isolates

The extended-spectrum-β-lactamase (ESBL) determinant CTX-M-55 is increasingly prevalent in Escherichia coli but remains extremely rare in Salmonella. This study reports the isolation of a plasmid harboring the bla_CTX-M-55 element in a clinical Salmonella enterica serotype Typhimurium strain resistant to multiple antibiotics. This plasmid is genetically identical to several known IncI2-type elements harbored by E. coli strains recovered from animals. This finding indicates that IncI2 plasmids harboring the bla_CTX-M genes may undergo cross-species migration among potential bacterial pathogens, with E. coli as the major source of such elements.