title: Expression of homologous RND efflux pump genes is dependent upon AcrB expression: implications for efflux and virulence inhibitor design.
abstract: OBJECTIVE
  Enterobacteriaceae have multiple efflux pumps that confer intrinsic resistance to antibiotics. AcrB mediates clinically relevant multidrug resistance and is required for virulence and biofilm formation, making it an attractive target for the design of inhibitors. The aim of this study was to assess the viability of single transporters as a target for efflux inhibition using Salmonella Typhimurium as the model pathogen.
  
  
  METHODS
  The expression of resistance-nodulation-division (RND) efflux pump genes in response to the inactivation of single or multiple homologues was measured using real-time RT-PCR. Phenotypes of mutants were characterized by measuring antimicrobial susceptibility, dye accumulation and the ability to cause infection in vitro.
  
  
  RESULTS
  The expression of all RND efflux pump genes was increased when single or multiple acr genes were inactivated, suggesting a feedback mechanism that activates the transcription of homologous efflux pump genes. When two or three acr genes were inactivated, the mutants had further reduced efflux, altered susceptibility to antimicrobials (including increased susceptibility to some, but conversely and counterintuitively, decreased susceptibility to some others) and were more attenuated in the tissue culture model than mutants lacking single pumps were.
  
  
  CONCLUSIONS
  These data indicate that it is critical to understand which pumps an inhibitor is active against and the effect of this on the expression of homologous systems. For some antimicrobials, an inhibitor with activity against multiple pumps will have a greater impact on susceptibility, but an unintended consequence of this may be decreased susceptibility to other drugs, such as aminoglycosides.
authors.affiliation: Antimicrobials Research Group, School of Immunity and Infection, College of Medical and Dental Sciences, and Institute of Microbiology and Infection, The University of Birmingham, Birmingham B15 2TT, UK.
authors.forename: Jessica M A
authors.initials: JM
authors.lastname: Blair
authors.affiliation: Antimicrobials Research Group, School of Immunity and Infection, College of Medical and Dental Sciences, and Institute of Microbiology and Infection, The University of Birmingham, Birmingham B15 2TT, UK.
authors.forename: Helen E
authors.initials: HE
authors.lastname: Smith
authors.affiliation: Antimicrobials Research Group, School of Immunity and Infection, College of Medical and Dental Sciences, and Institute of Microbiology and Infection, The University of Birmingham, Birmingham B15 2TT, UK.
authors.forename: Vito
authors.initials: V
authors.lastname: Ricci
authors.affiliation: Antimicrobials Research Group, School of Immunity and Infection, College of Medical and Dental Sciences, and Institute of Microbiology and Infection, The University of Birmingham, Birmingham B15 2TT, UK.
authors.forename: Amelia J
authors.initials: AJ
authors.lastname: Lawler
authors.affiliation: Antimicrobials Research Group, School of Immunity and Infection, College of Medical and Dental Sciences, and Institute of Microbiology and Infection, The University of Birmingham, Birmingham B15 2TT, UK.
authors.forename: Louisa J
authors.initials: LJ
authors.lastname: Thompson
authors.affiliation: Antimicrobials Research Group, School of Immunity and Infection, College of Medical and Dental Sciences, and Institute of Microbiology and Infection, The University of Birmingham, Birmingham B15 2TT, UK l.j.v.piddock@bham.ac.uk.
authors.forename: Laura J V
authors.initials: LJ
authors.lastname: Piddock
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D024901:Drug Resistance, Multiple, Bacterial / Q000187:drug effects / Q000235:genetics*; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial / Q000187:drug effects; D020868:Gene Silencing; D005838:Genotype; D026901:Membrane Transport Proteins / Q000235:genetics*; D008826:Microbial Sensitivity Tests; D005810:Multigene Family; D009154:Mutation; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics; D014774:Virulence / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D026901:Membrane Transport Proteins
keywords: AcrB; AcrD; AcrF; redundancy