AUTHOR=Wang Wei , Baloch Zulqarnain , Zou Mingyuan , Dong Yinping , Peng Zixin , Hu Yujie , Xu Jin , Yasmeen Nafeesa , Li Fengqin , Fanning Séamus 

TITLE=Complete Genomic Analysis of a Salmonella enterica Serovar Typhimurium Isolate Cultured From Ready-to-Eat Pork in China Carrying One Large Plasmid Containing mcr-1

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.00616

DOI=10.3389/fmicb.2018.00616

ISSN=1664-302X

ABSTRACT=<p>One <italic>mcr-1</italic>-carrying ST34-type <italic>Salmonella</italic> Typhimurium WW012 was cultured from 3,200 ready-to-eat (RTE) pork samples in 2014 in China. Broth dilution method was applied to obtain the antimicrobial susceptibility of <italic>Salmonella</italic> Typhimurium WW012. Broth matting assays were carried out to detect transferability of this phenotype and whole-genome sequencing was performed to analyze its genomic characteristic. Thirty out of 3,200 RTE samples were positive for <italic>Salmonella</italic> and the three most frequent serotypes were identified as <italic>S</italic>. Derby (<italic>n</italic> = 8), <italic>S</italic>. Typhimurium (<italic>n</italic> = 6), and <italic>S</italic>. Enteritidis (<italic>n</italic> = 6). One <italic>S</italic>. Typhimurium isolate (<italic>S</italic>. Typhimurium WW012) cultured from RTE prepared pork was found to contain the <italic>mcr-1</italic> gene. <italic>S</italic>. Typhimurium WW012 expressed a level of high resistance to seven different antimicrobial compounds in addition to colistin (MIC = 8 mg/L). A single plasmid, pWW012 (151,609-bp) was identified and found to be of an IncHI2/HI2A type that encoded a <italic>mcr-1</italic> gene along with six additional antimicrobial resistance genes. Plasmid pWW012 contained an IS<italic>30</italic>-<italic>mcr-1</italic>-<italic>orf</italic>-<italic>orf</italic>-IS<italic>30</italic> composite transposon that can be successfully transferred to <italic>Escherichia coli</italic> J53. When assessed further, the latter demonstrated considerable similarity to three plasmids pHYEC7-<italic>mcr-1</italic>, pSCC4, and pHNSHP45-2, respectively. Furthermore, plasmid pWW012 also contained a multidrug resistance (MDR) genetic structure IS<italic>26</italic>-<italic>aadA2</italic>-<italic>cmlA2</italic>-<italic>aadA1</italic>-IS<italic>406</italic>-<italic>sul3</italic>-IS<italic>26</italic>-<italic>dfrA12</italic>-<italic>aadA2</italic>-IS<italic>26</italic>, which showed high similarity to two plasmids, pHNLDF400 and pHNSHP45-2, respectively. Moreover, genes mapping to the chromosome (4,991,167-bp) were found to carry 28 mutations, related to two component regulatory systems (<italic>pmrAB, phoPQ</italic>) leading to modifications of lipid A component of the lipopolysaccharide structure. Additionally, one mutation (D87N) in the quinolone resistance determining region (QRDR) gene of <italic>gyrA</italic> was identified in this <italic>mcr-1</italic> harboring <italic>S</italic>. Typhimurium. In addition, various virulence factors and heavy metal resistance-encoding genes were also identified on the genome of <italic>S</italic>. Typhimurium WW012. This is the first report of the complete nucleotide sequence of <italic>mcr-1</italic>-carrying MDR <italic>S</italic>. Typhimurium strain from RTE pork in China.</p>