mcr-1 facilitated selection of high-level colistin-resistant mutants in Escherichia coli

Abstract

a b s t r a c tObjectives: The mcr-1 gene is the first reported plasmid-mediated colistin resistance gene. It has caused worldwide concern about the colistin resistance in Gram-negative bacteria. The aim of this research was to study the impact of mcr-1 on the selection of high-level colistin resistance (HLCR) mutations in Escherichia coli and Klebsiella pneumoniae. Methods: We detected the HLCR mutation rates of Enterobacteriaceae strains (K. pneumoniae XH209, KP10, and E. coli Q3, ATCC 25922) and their transformants harbouring the mcr-1 gene. Further analysis of the HLCR mutants was conducted by sequencing, plasmid elimination experiment, and real-time quantitative PCR. Results: For XH209, mean mutation rate of XH209-pMCR was 1.7 (95% confidence interval (CI) 0.76 e2.54) Â 10 À8 , while XH209 and XH209-pCR2.1 showed mutation rates of 2.0 (95% CI, 1.32e2.67) Â 10 À8 and 2.3 (95% CI 1.47e3.13) Â 10 À8 . For KP10 and its derived strains KP10-pCR2.1, KP10-pMCR, the mutation rates were 3.5 (95% CI 0.77e6.13) Â 10 À8 , 4.8 (95% CI 0.69e8.94) Â 10 À8 and 4.2 (95% CI 0.95 e7.54) Â 10 À8 respectively. The mutation rates of E. coli strains Q3-pMCR and ATCC25922-pMCR were 3.4 (95% CI 0.19e7.47) Â 10 À8 and 1.54 (95% CI 0.27e2.8) Â 10 À9 , which were significantly higher than their corresponding non-mcr-1-carrying strains (p < 0.05). Conclusions: Beside the knowledge that mcr-1 mediates low-level colistin resistance, this gene also facilitates selection of HLCR mutants in E. coli, but does not affect K. pneumoniae. H. Zhang, Clin Microbiol Infect 2019;25:517.e1e517.e4

Colistin Resistance in Enterobacterales Strains – A Current View

“…Generally, E. coli strains with the mcr-1 gene are characterized by the low-level colistin resistance with a minimum inhibitory concentration (MIC) in the range of 2-8 mg/l. Zhang et al (2019) have shown that the expression of the mcr-1 gene in E. coli led to a higher mutation rate in the chromosomal polymyxin resistance cascade genes and produced higher MIC values (≥ 64 mg/l).…”

Sequence Duplication Within pmrB Gene Contribute to High-Level Colistin Resistance in Avian Pathogenic Escherichia coli

“…24,25,40,42 In addition, a very recent report showed that pmrAB mutations contribute to the selection of HLCR in E. coli. 31 Currently, HLCR mechanisms have been…”

“…Figure 1 and Supplementary Table S2 shows the domains of PmrA/PmrB and positions of induced mutations conferring colistin resistance in this study as well as previously published mutations. 24,25,31,39,40 After subculturing in the absence of colistin, the PmrB-sd mutants IND-91 and IND-107 showed no reduction of colistin MIC, suggesting that the acquisition of this resistance phenotype was stable.…”

“…[26][27][28][29][30] Recently, a study indicates that the acquisition of mcr-1 can facilitate the selection of high-level colistin-resistant (minimum inhibitory concentration [MIC] ‡32 mg/L) mutations in PmrAB of E. coli. 31 However, the underlying mechanisms involved in HLCR remain to be discovered. In this study, we identified HLCR mutations from colistinsusceptible APEC isolates after colistin exposure and revealed that two novel mutations of sequence duplication within pmrB gene ( pmrB-sd) contribute to HLCR by using comprehensive approaches.…”

Data_Sheet_1.docx

“…It seems that K. pneumoniae is more likely to generate chromosomal mutations but is less likely to harbor mcr-1 compared to the phenomenon observed in E. coli. Nevertheless, a previous study showed that after a single overnight exposure to twofold minimum inhibitory concentrations (MICs) of colistin, mcr-1 facilitated the development of high-level colistin resistance (HLCR; MIC ≥ 32 mg/L) mutants in E. coli but did not affect the HLCR mutation rates in K. pneumoniae (Zhang et al, 2019). However, another study reported that MCR-negative strains could be induced to higher level of colistin resistance than MCR-positive strains after step-wise induction (Luo et al, 2019).…”