Characteristics of Carbapenem-Resistant and Colistin-Resistant Escherichia coli Co-Producing NDM-1 and MCR-1 from Pig Farms in China

Abstract

The emergence of carbapenem-resistant and colistin-resistant <i>Enterobacteriaceae</i> represents a great risk for public health. In this study, the phenotypical and genetic characteristics of eight carbapenem-resistant and colistin-resistant isolates from pig farms in China were determined by the broth microdilution method and whole genome sequencing. Antimicrobial susceptibility testing showed that the eight carbapenem-resistant and colistin-resistant strains were resistant to three aminoglycosides, twelve β-lactams, one of the phenicols, one of the tetracyclines, and one of the fluoroquinolones tested, simultaneously. The prediction of acquired resistant genes using the whole genome sequences revealed the co-existence of <i>bla</i>_NDM-1 and <i>mcr-1</i> as well as the other genes that were responsible for the multidrug-resistant phenotypes. Bioinformatics analysis also showed that the carbapenem-resistant gene <i>bla</i>_NDM-1 was located on a putative IncFII-type plasmid, which also carried the other acquired resistant genes identified, including <i>fosA3</i>, <i>blaTEM-1B</i> and <i>rmtB</i>, while the colistin-resistant gene <i>mcr-1</i> was carried by a putative IncX4-type plasmid. Finally, we found that these resistant genes/plasmids were conjugative, and they could be co-conjugated, conferring resistance to multiple types of antibiotics, including the carbapenems and colistin, to the recipient <i>Escherichia</i> <i>coli</i> strains.