Characterization of two novel colistin resistance gene variants originated from spp.

This study aimed to characterize two novel variants, and , which originated from spp. that were isolated from diseased pigs in China. The spp. carrying novel variants were subjected to whole-genome sequencing (WGS) and phylogenetic analysis based on the 16S rRNA gene. The variants and were characterized using phylogenetic analysis, a comparison of genetic environments, and protein structure prediction. The WGS indicated that two novel variants were located in the chromosomes of three spp. with a genetic environment of -. In addition to the novel colistin resistance genes and , the three spp. contained other antimicrobial resistance genes, including , (O), , , and . A functional cloning assay indicated that either the or gene could confer resistance to colistin in DH5α and JM109. The nucleotide sequences of and presented 95.33 and 95.33% identities, respectively, to . The phylogenetic analysis showed that and were derived from spp. that belonged to subclades that were different from those of the variants ( to except ) originating from Enterobacteriaceae. The deduced amino acid sequences of MCR-1.35 (MCR-1.36) showed 96.67% (96.49%), 82.59% (82.04%), 84.07% (83.52%), 55.52% (55.17%), 59.75% (59.57%), and 61.88% (61.69%) identity to MCR-1.10, MCR-2.2, MCR-6.1, MCR-LIN, MCR-OSL, and MCR-POR, respectively, that originated from sp. Notably, protein structure alignment showed only a few changes in amino acid residues between MCR-1.1 and MCR-1.35, as well as between MCR-1.1 and MCR-1.36. In conclusion, this study identified spp. carrying two novel variants, and , conferring resistance to colistin, which were isolated from pig farms in China. In addition, -like variants were observed to be located in the chromosomes of some species of isolated from pig samples.