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J Antimicrob Chemother. 2017 Oct 1;72(10):2729-2736. doi: 10.1093/jac/dkx204.

Modifications in the pmrB gene are the primary mechanism for the development of chromosomally encoded resistance to polymyxins in uropathogenic Escherichia coli.

Author information

1
School of Chemistry & Molecular Biosciences, The University of Queensland, Brisbane, Queensland, Australia.
2
Australian Infectious Diseases Research Centre, The University of Queensland, Brisbane, Queensland, Australia.
3
Australian Centre for Ecogenomics, The University of Queensland, Brisbane, Queensland, Australia.
4
Division of Genetics and Molecular Biology, Institute of Biological Sciences, Faculty of Science, University of Malaya, 50603 Kuala, Lumpur, Malaysia.
5
The University of Queensland Centre for Clinical Research, The University of Queensland, Brisbane, Queensland, Australia.

Abstract

Objectives:

Polymyxins remain one of the last-resort drugs to treat infections caused by MDR Gram-negative pathogens. Here, we determined the mechanisms by which chromosomally encoded resistance to colistin and polymyxin B can arise in the MDR uropathogenic Escherichia coli ST131 reference strain EC958.

Methods:

Two complementary approaches, saturated transposon mutagenesis and spontaneous mutation induction with high concentrations of colistin and polymyxin B, were employed to select for mutations associated with resistance to polymyxins. Mutants were identified using transposon-directed insertion-site sequencing or Illumina WGS. A resistance phenotype was confirmed by MIC and further investigated using RT-PCR. Competitive growth assays were used to measure fitness cost.

Results:

A transposon insertion at nucleotide 41 of the pmrB gene (EC958pmrB41-Tn5) enhanced its transcript level, resulting in a 64- and 32-fold increased MIC of colistin and polymyxin B, respectively. Three spontaneous mutations, also located within the pmrB gene, conferred resistance to both colistin and polymyxin B with a corresponding increase in transcription of the pmrCAB genes. All three mutations incurred a fitness cost in the absence of colistin and polymyxin B.

Conclusions:

This study identified the pmrB gene as the main chromosomal target for induction of colistin and polymyxin B resistance in E. coli.

PMID:
29091192
DOI:
10.1093/jac/dkx204
[Indexed for MEDLINE]

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