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

SIMPLE SUMMARY: The prevalence of extended-spectrum cephalosporin (ESC)-resistant Salmonella is of great concern, as these strains with the same β-lactamase (bla) genes were found in human and poultry. The objective is to characterize ESC-resistant Salmonella isolated from chicken and to determine the transferability of β-lactamase gene-harboring plasmid in vitro and in vivo. ESC resistance genes in Salmonella isolated from chickens and presented a comprehensive analysis of the highly frequent transfer of the bla(CMY-2) gene in vitro and in vivo. In addition, this study has demonstrated the ease with which a bla(CMY-2) gene-harboring plasmid can be rapidly transferred between Salmonella and pathogenic E. coli within the intestinal tracts of mice, even without antimicrobial selective pressure. Given the potential risk of the frequent transfer of the bla(CMY-2) gene via the food chain to the human digestive tract, the molecular mechanism involved in the dissemination and maintenance of ESC resistance genes should be studied as further research in greater detail, and enhanced surveillance should be implemented to prevent the widespread of ESC resistant strains. 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; bla(CTX-M-15) was the most prevalent gene and two strains carried bla(TEM-1)/bla(CTX-M-15) and bla(CMY-2), respectively. The transferable bla(CTX-M-15) gene was carried by IncFII plasmid in three isolates and the bla(CMY-2) gene carried by IncI1 plasmid in one isolate. bla(CMY-2) gene-harboring strain was selected as the donor based on the high frequency of bla(CMY-2) gene transfer in vitro and its transfer frequencies were determined at 10(−3) transconjugants per recipient. The transfer of bla(CMY-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; bla(CMY-2) gene-harboring transconjugant showed variable fitness burden depends on the parent strains. Our study demonstrated direct evidence that the bla(CMY-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.