Characterization of Extended-Spectrum Cephalosporin (ESC) Resistance in <i>Salmonella</i> Isolated from Chicken and Identification of High Frequency Transfer of <i>bla</i>_CMY-2 Gene Harboring Plasmid In Vitro and In Vivo

Abstract

A total of 136 Salmonella isolates from chicken feces and meat samples of the top 12 integrated chicken production companies throughout Korea were collected. Among the 17 ESC-resistant Salmonella; blaCTX-M-15 was the most prevalent gene and two strains carried blaTEM-1/blaCTX-M-15 and blaCMY-2, respectively. The transferable blaCTX-M-15 gene was carried by IncFII plasmid in three isolates and the blaCMY-2 gene carried by IncI1 plasmid in one isolate. blaCMY-2 gene-harboring strain was selected as the donor based on the high frequency of blaCMY-2 gene transfer in vitro and its transfer frequencies were determined at 10−3 transconjugants per recipient. The transfer of blaCMY-2 gene-harboring plasmid derived from chicken isolate into a human pathogen; enteroinvasive Escherichia coli (EIEC), presented in mouse intestine with about 10−1 transfer frequency without selective pressure. From the competition experiment; blaCMY-2 gene-harboring transconjugant showed variable fitness burden depends on the parent strains. Our study demonstrated direct evidence that the blaCMY-2 gene harboring Salmonella from chicken could frequently transfer its ESC-resistant gene to E. coli in a mouse intestine without antimicrobial pressure; resulting in the emergence of multidrug resistance in potentially virulent EIEC isolates of significance to human health; which can increase the risk of therapeutic inadequacy or failures.

Keywords

• <i>Salmonella</i>
• chicken
• extended-spectrum cephalosporin
• <i>bla</i>_CMY-2
• mouse
• frequent transfer