AUTHOR=Che Yongliang , Wu Renjie , Li Hongjie , Wang Longbai , Wu Xuemin , Chen Qiuyong , Chen Rujing , Zhou Lunjiang 

TITLE=Characterization of two novel colistin resistance gene mcr-1 variants originated from Moraxella spp.

JOURNAL=Frontiers in Microbiology

VOLUME=14

YEAR=2023

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2023.1153740

DOI=10.3389/fmicb.2023.1153740

ISSN=1664-302X

ABSTRACT=<p>This study aimed to characterize two novel <italic>mcr-1</italic> variants, <italic>mcr-1.35</italic> and <italic>mcr-1.36</italic>, which originated from <italic>Moraxella</italic> spp. that were isolated from diseased pigs in China. The <italic>Moraxella</italic> spp. carrying novel <italic>mcr-1</italic> variants were subjected to whole-genome sequencing (WGS) and phylogenetic analysis based on the 16S rRNA gene. The <italic>mcr-1</italic> variants <italic>mcr-1.35</italic> and <italic>mcr-1.36</italic> were characterized using phylogenetic analysis, a comparison of genetic environments, and protein structure prediction. The WGS indicated that two novel <italic>mcr-1</italic> variants were located in the chromosomes of three <italic>Moraxella</italic> spp. with a genetic environment of <italic>mcr-1</italic>-<italic>pap2</italic>. In addition to the novel colistin resistance genes <italic>mcr-1.35</italic> and <italic>mcr-1.36</italic>, the three <italic>Moraxella</italic> spp. contained other antimicrobial resistance genes, including <italic>aac(3)-IId</italic>, <italic>tet</italic>(O), <italic>sul2</italic>, <italic>floR</italic>, and <italic>bla</italic><sub>ROB-3</sub>. A functional cloning assay indicated that either the <italic>mcr-1.35</italic> or <italic>mcr-1.36</italic> gene could confer resistance to colistin in <italic>Escherichia coli</italic> DH5α and JM109. The nucleotide sequences of <italic>mcr-1.35</italic> and <italic>mcr-1.36</italic> presented 95.33 and 95.33% identities, respectively, to <italic>mcr-1.1</italic>. The phylogenetic analysis showed that <italic>mcr-1.35</italic> and <italic>mcr-1.36</italic> were derived from <italic>Moraxella</italic> spp. that belonged to subclades that were different from those of the <italic>mcr-1</italic> variants (<italic>mcr-1.1</italic> to <italic>mcr-1.34</italic> except <italic>mcr-1.10</italic>) 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 <italic>Moraxella</italic> 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 <italic>Moraxella</italic> spp. carrying two novel <italic>mcr-1</italic> variants, <italic>mcr-1.35</italic> and <italic>mcr-1.36</italic>, conferring resistance to colistin, which were isolated from pig farms in China. In addition, <italic>mcr</italic>-like variants were observed to be located in the chromosomes of some species of <italic>Moraxella</italic> isolated from pig samples.</p>