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Original article
Aminoglycoside resistance of Pseudomonas aeruginosa in cystic fibrosis results from convergent evolution in the mexZ gene
  1. Michelle H Prickett1,
  2. Alan R Hauser1,
  3. Susanna A McColley1,2,
  4. Joanne Cullina2,
  5. Eileen Potter2,
  6. Cathy Powers2,
  7. Manu Jain1
  1. 1Feinberg School of Medicine, Northwestern University, Chicago, Illinois, USA
  2. 2Ann & Robert H. Lurie Children's Hospital of Chicago, Chicago, Illinois, USA
  1. Correspondence to Dr Manu Jain, Division of Pulmonary and Critical Care Medicine, Feinberg School of Medicine, Northwestern University, 240 E. Huron Avenue, McGaw M-332, Northwestern University, Chicago, IL 60611, USA; m-jain{at}northwestern.edu

Abstract

Rationale Aminoglycoside (AG) resistance of Pseudomonas aeruginosa in cystic fibrosis (CF) is associated with poorer clinical outcomes and is usually due to overexpression of the efflux pump MexXY. MexXY is regulated by mexZ, one of the most commonly mutated genes in CF P. aeruginosa isolates. Little is known about the evolutionary relationship between AG resistance, MexXY expression and mexZ mutations.

Objectives To test the hypothesis that AG resistance in P. aeruginosa develops in parallel with higher MexXY expression and mexZ mutations.

Methods CF P. aeruginosa isolates were compared for chronically infected (CI) adults, CI children and children with new infection.

Measurements One P. aeruginosa isolate from each patient was analysed for mexZ mutations, mexY mRNA expression and amikacin resistance.

Main results 56 patients with CF were enrolled: 21 children with new P. aeruginosa infection, 18 CI children and 17 CI adults. Amikacin resistance and mexY mRNA expression were higher in cohorts with longer P. aeruginosa infection. The prevalence of non-conservative mexZ mutations was 0%, 33% and 65% in children with new infection, CI children and CI adults, respectively. The same trend was seen in the ratio of non-conservative to non-synonymous mexZ mutations. Of isolates with non-conservative mexZ mutations, 59% were amikacin-resistant compared with 18% of isolates with non-synonymous mutations. The doubling rate of amikacin resistance and non-conservative mexZ mutations was approximately 5 years.

Conclusions P. aeruginosa mexZ mutations undergo positive selection resulting in increased mexY mRNA expression and amikacin resistance and likely play a role in bacterial adaption in the CF lung.

  • Cystic Fibrosis
  • Respiratory Infection
  • Bacterial Infection
  • Bronchiectasis

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Footnotes

  • Funding National Center for Advancing Translational Sciences (grant number: 8UL1TR000150); Cystic Fibrosis Foundation (grant number: Fellow Research Training Grant).

  • Competing interests None declared.

  • Ethics approval Northwestern University IRB, Lurie Children's IRB.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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