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

Area of Science:

• Microbiology
• Antimicrobial Resistance
• Molecular Biology

Background:

• Extended-spectrum-β-lactamase (ESBL) determinants, particularly CTX-M-55, are increasingly common in *Escherichia coli*.
• CTX-M-55 is exceptionally rare in *Salmonella* species.
• The emergence of antibiotic resistance in bacterial pathogens is a significant global health concern.

Purpose of the Study:

• To report the identification of a plasmid carrying the *bla*CTX-M-55 gene in a clinical isolate of *Salmonella enterica* serotype Typhimurium.
• To characterize the genetic relatedness of this plasmid to known elements in other bacterial species.

Main Methods:

• Plasmid isolation and sequencing from a multi-drug resistant *Salmonella Typhimurium* clinical strain.
• Comparative genomic analysis of the isolated plasmid against existing databases.
• Identification of plasmid type and genetic elements, including the *bla*CTX-M-55 gene.

Main Results:

• A plasmid harboring the *bla*CTX-M-55 ESBL determinant was successfully isolated from a clinical *Salmonella Typhimurium* strain.
• The identified plasmid was found to be genetically identical to IncI2-type plasmids previously identified in *Escherichia coli* strains from animal sources.
• This represents a rare instance of CTX-M-55 detection in *Salmonella*.

Conclusions:

• IncI2 plasmids carrying *bla*CTX-M genes can facilitate cross-species transmission between bacterial pathogens.
• *Escherichia coli* serves as a potential major reservoir and source for the dissemination of these ESBL-encoding plasmids to other species, including *Salmonella*.
• This finding highlights the potential for the spread of antibiotic resistance determinants through horizontal gene transfer.