title: Molecular analysis of the ramRA locus in clinical Klebsiella pneumoniae isolates with reduced susceptibility to tigecycline.
abstract: Mutations in ramR, a negative regulator of ramA which stimulates transcription of acrA/-B encoding the multidrug efflux pump AcrAB-TolC, were recently shown to result in reduced susceptibility to tigecycline in Klebsiella pneumoniae. We analysed six non-duplicate K. pneumoniae isolates with elevated MICs to tigecycline. All isolates showed transcriptional up-regulation of ramA and acrB as demonstrated by Northern blot and quantitative real-time PCR. Sequencing of the ramR gene revealed deletions in five of the isolates and a premature stop codon in one isolate. Transformation of the wild-type ramR gene but not of any of the detected mutant ramR genes into a ramR-mutant K. pneumoniae strain restored tigecycline susceptibility and repressed ramA and acrB transcription to wild type levels. Thus, our study confirms the role of inactivating mutations in the ramR gene in tigecycline resistance.
authors.affiliation: Institute of Medical Microbiology, Virology and Hygiene, University Medical Centre Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Cristina Belmar
authors.initials: CB
authors.lastname: Campos
authors.affiliation: Institute of Medical Microbiology, Virology and Hygiene, University Medical Centre Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Martin
authors.initials: M
authors.lastname: Aepfelbacher
authors.affiliation: Institute of Medical Microbiology, Virology and Hygiene, University Medical Centre Hamburg-Eppendorf, Hamburg, Germany.|MVZ Labor Dr. Fenner und Kollegen, Bergstrasse 14, 20095 Hamburg.
authors.forename: Moritz
authors.initials: M
authors.lastname: Hentschke
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D024881:Drug Resistance, Bacterial; D015964:Gene Expression Regulation, Bacterial / Q000502:physiology; D007711:Klebsiella pneumoniae / Q000187:drug effects* / Q000235:genetics*; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D000078304:Tigecycline
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D000078304:Tigecycline; D008911:Minocycline
keywords: RamR; Tigecycline; efflux; resistance