Impact of OqxR loss of function on the envelope proteome of Klebsiella pneumoniae and susceptibility to antimicrobials

Wan Nur Ismah Wan Ahmad Kamil, Yuiko Takebayashi, Jacqueline Findlay, Kate Heesom, Matthew Avison

Research output: Contribution to journalArticle (Academic Journal)peer-review

9 Citations (Scopus)
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BACKGROUND: In Klebsiella pneumoniae, loss-of-function mutations in the transcriptional repressors RamR and OqxR both have an impact on the production of efflux pumps and porins relevant to antimicrobial efflux/entry. OBJECTIVES: To define, in an otherwise isogenic background, the relative effects of OqxR and RamR loss-of-function mutations on envelope protein production, envelope permeability and antimicrobial susceptibility. We also investigated the clinical relevance of an OqxR loss-of-function mutation, particularly in the context of β-lactam susceptibility. METHODS:  Envelope permeability was estimated using a fluorescent dye accumulation assay. Antimicrobial susceptibility was measured using disc testing. Total envelope protein production was quantified using LC-MS/MS proteomics and quantitative RT-PCR was used to measure transcript levels.RESULTS:Loss of RamR or OqxR reduced envelope permeability in K. pneumoniae by 45%-55% relative to the WT. RamR loss activated AcrAB efflux pump production ∼5-fold and this reduced β-lactam susceptibility, conferring ertapenem non-susceptibility even in the absence of a carbapenemase. In contrast, OqxR loss specifically activated OqxAB efflux pump production >10 000-fold. This reduced fluoroquinolone susceptibility but had little impact on β-lactam susceptibility even in the presence of a β-lactamase.CONCLUSIONS:Whilst OqxR loss and RamR loss are both seen in K. pneumoniae clinical isolates, only RamR loss significantly stimulates AcrAB efflux pump production. This means that only RamR mutants have significantly reduced β-lactamase-mediated β-lactam susceptibility and therefore represent a greater clinical threat.
Original languageEnglish
Article numberdky293
Pages (from-to)2990-2996
Number of pages7
JournalJournal of Antimicrobial Chemotherapy
Issue number11
Early online date24 Jul 2018
Publication statusPublished - 1 Nov 2018


  • Klebsiella pneumoniae
  • Efflux Pumps
  • Proteomics
  • Gene regulation


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