title: MarA-mediated overexpression of the AcrAB efflux pump results in decreased susceptibility to tigecycline in Escherichia coli.
abstract: OBJECTIVE
  The purpose of this study was to characterize decreased susceptibility to tigecycline in clinical isolates of Escherichia coli obtained during Phase 3 clinical trials.
  
  
  METHODS
  Gene expression was analysed by transcriptional profile analysis and RT-PCR. Transposon mutagenesis with IS903kan was used for selection of transposon mutants. Transposon insertions were mapped by DNA sequencing and PCR analyses. The MICs were determined by broth microdilution.
  
  
  RESULTS
  Both transcriptional profile analysis and Taqman RT-PCR demonstrated increased expression levels of MarA, a transcriptional activator, and AcrAB, an RND-type efflux pump, in the strains with elevated tigecycline MICs. Transposon mutagenesis generated nine mutants, the majority of which had either marA or acrB inactivated. Sequence analysis revealed a single nucleotide insertion in the open reading frame of the marR gene in less-susceptible strains of E. coli.
  
  
  CONCLUSIONS
  This study suggested that a loss of MarR functionality due to a frameshift mutation resulted in constitutive overproduction of MarA and AcrAB and, consequently, in decreased susceptibility to tigecycline in clinical isolates of E. coli.
authors.affiliation: Wyeth Research, Pearl River, NY, USA. keeneyd@wyeth.com
authors.forename: David
authors.initials: D
authors.lastname: Keeney
authors.forename: Alexey
authors.initials: A
authors.lastname: Ruzin
authors.forename: Fionnuala
authors.initials: F
authors.lastname: McAleese
authors.forename: Ellen
authors.initials: E
authors.lastname: Murphy
authors.forename: Patricia A
authors.initials: PA
authors.lastname: Bradford
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000096:biosynthesis / Q000235:genetics; D001426:Bacterial Proteins / Q000096:biosynthesis / Q000235:genetics; D001483:Base Sequence; D004251:DNA Transposable Elements / Q000235:genetics; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics; D024881:Drug Resistance, Bacterial / Q000187:drug effects* / Q000235:genetics; D004926:Escherichia coli / Q000187:drug effects / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000096:biosynthesis / Q000235:genetics*; D016368:Frameshift Mutation; D008074:Lipoproteins / Q000096:biosynthesis / Q000235:genetics; D026901:Membrane Transport Proteins / Q000096:biosynthesis / Q000235:genetics; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000031:analogs & derivatives* / Q000494:pharmacology; D008969:Molecular Sequence Data; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000096:biosynthesis / Q000235:genetics; D016366:Open Reading Frames; D012329:RNA, Bacterial / Q000235:genetics; D000078304:Tigecycline
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D008074:Lipoproteins; D026901:Membrane Transport Proteins; D008911:Minocycline; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D012329:RNA, Bacterial; D000078304:Tigecycline; C083497:AcrA protein, E coli; C083496:AcrB protein, E coli; C080002:MarA protein, E coli; C080003:multiple antibiotic resistance protein B; C073126:tolC protein, E coli