AUTHOR=Liu Ruishan , Xu Hao , Guo Xiaobing , Liu Shuxiu , Qiao Jie , Ge Haoyu , Zheng Beiwen , Gou Jianjun 

TITLE=Genomic Characterization of Two Escherichia fergusonii Isolates Harboring mcr-1 Gene From Farm Environment

JOURNAL=Frontiers in Cellular and Infection Microbiology

VOLUME=12

YEAR=2022

URL=https://www.frontiersin.org/journals/cellular-and-infection-microbiology/articles/10.3389/fcimb.2022.774494

DOI=10.3389/fcimb.2022.774494

ISSN=2235-2988

ABSTRACT=<p>The prevalence and transmission of mobile colistin resistance (<italic>mcr</italic>) genes have led to a severe threat to humans and animals. <italic>Escherichia fergusonii</italic> is an emerging pathogen which is closely related to a variety of diseases. However, the report of <italic>mcr</italic> genes harboring <italic>E. fergusonii</italic> is still rare. One study in Brazil reported the <italic>E. fergusonii</italic> isolates with IncHI2-type plasmids harboring <italic>mcr-1</italic>. A Chinese study reported two strains carrying <italic>mcr-1</italic> gene with the same plasmid type IncI2. Here, we identified two strains of <italic>E. fergusonii</italic> carrying <italic>mcr-1</italic> gene from farm environments with IncX4-type and IncI2-type plasmids, respectively. To our best knowledge, this is the first report about <italic>mcr-1</italic> gene located on IncX4-type plasmid in <italic>E. fergusonii</italic>. We investigate the resistance mechanism of colistin-resistant <italic>Escherichia fergusonii</italic> strains 6S41-1 and 5ZF15-2-1 and elucidate the genetic context of plasmids carrying <italic>mcr-1</italic> genes. In addition, we also investigated chromosomal mutations mediated colistin resistance in these two strains. Species identification was performed using MALDI-TOF MS and 16S rRNA gene sequencing. The detection of <italic>mcr-1</italic> gene was determined by PCR and Sanger sequencing. S1-pulsed-field gel electrophoresis (PFGE), Southern blotting, antimicrobial susceptibility testing, conjugation experiments, complete genome sequencing, and core genome analysis were conducted to investigate the characteristics of isolates harboring <italic>mcr-1</italic>. The <italic>mcr-1</italic> genes on two strains were both plasmids encoded and the typical IS<italic>26</italic>-<italic>parA</italic>-<italic>mcr-1</italic>-<italic>pap2</italic> cassette was identified in p6S41-1 while a <italic>nikA</italic>-<italic>nikB</italic>-<italic>mcr-1</italic> locus sites on the conjugative plasmid p5ZF15-2-1. In addition, Core genome analysis reveals that <italic>E. fergusonii</italic> 6S41-1 and 5ZF15-2-1 have close genetic relationships. The <italic>mcr-1</italic> gene is located on conjugative IncI2-type plasmid p5ZF15-2-1, which provides support for its further transmission. In addition, there’s the possibility of <italic>mcr-1</italic> spreading to humans through farm environments and thereby threatening public health. Therefore, continuous monitoring and investigations of <italic>mcr-1</italic> among <italic>Enterobacteriaceae</italic> in farm environments are necessary to control the spread.</p>