Expression characteristics of the plasmid-borne mcr-1 colistin resistance gene
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Haifang Zhang1,*, Minhui Miao1,*, Jieting Yan1,*, Min Wang1, Yi-Wei Tang2, Barry N. Kreiswirth3, Xia Zhang4, Liang Chen3 and Hong Du1
1Department of Clinical Laboratory, The Second Affiliated Hospital of Soochow University, Suzhou, Jiangsu 215004, China
2Department of Laboratory Medicine, Memorial Sloan Kettering Cancer Center, Department of Pathology and Laboratory Medicine, Weill Medical College of Cornell University, New York, New York 10065, USA
3Public Health Research Institute TB Center, Rutgers University, Newark, New Jersey 07103, USA
4Department of Clinical Laboratory, The North District of Affiliated Suzhou Hospital, Nanjing Medical University, Suzhou 215008, Jiangsu Province, China
*These authors contributed equally to this work
Hong Du, email: email@example.com
Liang Chen, email: Chen11@njms.rutgers.edu
Xia Zhang, email: firstname.lastname@example.org
Keywords: mcr-1; colistin; gene expression; regulation; plasmid
Received: August 10, 2017 Accepted: October 28, 2017 Published: November 20, 2017
The plasmid-encoded colistin resistance gene (mcr-1) has recently been reported in various Gram-negative species. However, the expression profile of mcr-1 remains unknown. Here, we investigated the expression of mcr-1 in various plasmids and bacteria. The mcr-1 expression levels in pMCR1_IncX4 varied from 1.81 × 10–5 to 1.05 × 10–4 (pmol per μg total RNA) in the two K. pneumoniae strains SZ03 and SZ04 (ST25) and the two E. coli strains SZ01 and CDA6 (ST2448 and ST167, respectively). The mcr-1 expression levels of pMCR1_IncI2 in E. coli SZ02 (ST2085) and E. coli BJ13 (ST457) were 5.27 × 10–5 and 2.58 × 10–5, respectively. In addition, the expression of chromosomal mcr-1 in ST156 E. coli BJ10 was 5.49×10–5. Interestingly, after 4μg/ml colistin treatment, mcr-1 in pMCR1_IncX4 increased 2- and 4-fold at 20 and 120 mins, respectively, in all pMCR1_IncX4-harboring strains, except for ST2448 E. coli, which had a lower expression after 20 mins that restored to baseline levels after 120 mins. In contrast, mcr-1 expression of pMCR1_IncI2 in the two E. coli strains (SZ02, BJ13) and the chromosomal mcr-1 in E. coli (BJ10) remained at baseline levels after 20 and 120 mins. In the same genetic background host strain E. coli E600, mcr-1 expression of pMCR1_IncX4 and pMCR1_IncI2 were similar and were decreased after colistin treatment for 20 min. However, mcr-1 in pMCR1_IncX4 was up-regulated after colistin treatment for 120 min, while mcr-1 in pMCR1_IncI2 was down-regulated compared to the untreated control. Our results suggested that mcr-1 has distinct expression profiles on different plasmids, bacterial hosts, and after antibiotic treatment.
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