Expression characteristics of the plasmid-borne mcr-1 colistin resistance gene.

Haifang Zhang,Yi-Wei Tang,Min Wang,Minhui Miao,Hong Du,Jieting Yan,Barry N Kreiswirth,Xia Zhang,Liang Chen

doi:10.18632/oncotarget.22538

Abstract

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.

Highlights

Multidrug-resistant Gram-negative bacteria, carbapenem-resistant Enterobacteriaceae (CRE), have spread globally into hospitals and communities, and have become a significant public health concern [1, 2]
Our results suggested that mcr-1 has distinct expression profiles on different plasmids, bacterial hosts, and after antibiotic treatment
The recent identification of a plasmid-encoded polymyxin resistance mechanism (MCR-1) in Enterobacteriaceae from both human and animal samples suggests that this last-resort antibiotic may be under jeopardy [3, 4]

Summary

INTRODUCTION

Multidrug-resistant Gram-negative bacteria, carbapenem-resistant Enterobacteriaceae (CRE), have spread globally into hospitals and communities, and have become a significant public health concern [1, 2]. The recent identification of a plasmid-encoded polymyxin resistance mechanism (MCR-1) in Enterobacteriaceae from both human and animal samples suggests that this last-resort antibiotic may be under jeopardy [3, 4]. The plasmid-transferrable mobilized colistin resistance gene mcr-1, encoding a novel PEA-transferase [3, 4], is able to mediate a PEA addition to the lipid A moiety at the 4ʹ-phosphate group, thereby causing colistin resistance. We completely sequenced mcr-1harboring plasmids pMCR1_IncX4 and pMCR1_IncI2 from clinical K. pneumoniae and E. coli strains [12]. We used quantitative reverse transcription PCR (qRT-PCR) to evaluate the expressions of mcr-1 of different plasmids (pMCR1_ IncX4 and pMCR1_IncI2) within different species (E. coli and K. pneumoniae) and their changes in response to colistin challenge

RESULTS

DISCUSSION

MATERIALS AND METHODS