title: Inhibition of multidrug efflux as a strategy to prevent biofilm formation.
abstract: OBJECTIVE
  We have recently shown that inactivation of any of the multidrug efflux systems of Salmonella results in loss of the ability to form a competent biofilm. The aim of this study was to determine the mechanism linking multidrug efflux and biofilm formation, and to determine whether inhibition of efflux is a viable antibiofilm strategy.
  
  
  METHODS
  Mutants lacking components of the AcrAB-TolC system in Salmonella enterica serovar Typhimurium were investigated for their ability to aggregate, produce biofilm matrix components and form a biofilm. The potential for export of a biofilm-relevant substrate via efflux pumps was investigated and expression of genes that regulate multidrug efflux and production of biofilm matrix components was measured. The ability of efflux inhibitors carbonyl cyanide m-chlorophenylhydrazone, chlorpromazine and phenyl-arginine-β-naphthylamide to prevent biofilm formation by Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus under static and flow conditions was assessed.
  
  
  RESULTS
  Mutants of Salmonella Typhimurium that lack TolC or AcrB, but surprisingly not AcrA, were compromised in their ability to form biofilms. This defect was not related to changes in cellular hydrophobicity, aggregative ability or export of any biofilm-specific factor. The biofilm defect resulted from transcriptional repression of curli biosynthesis genes and consequent inhibition of production of curli. All three efflux inhibitors significantly reduced biofilm production in both static and flow biofilm assays, although different concentrations of each inhibitor were most active against each species.
  
  
  CONCLUSIONS
  This work shows that both genetic inactivation and chemical inhibition of efflux pumps results in transcriptional repression of biofilm matrix components and a lack of biofilm formation. Therefore, inhibition of efflux is a promising antibiofilm strategy.
authors.affiliation: School of Immunity and Infection, Institute for Microbiology and Infection, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
authors.forename: Stephanie
authors.initials: S
authors.lastname: Baugh
authors.forename: Charlotte R
authors.initials: CR
authors.lastname: Phillips
authors.forename: Aruna S
authors.initials: AS
authors.lastname: Ekanayaka
authors.forename: Laura J V
authors.initials: LJ
authors.lastname: Piddock
authors.forename: Mark A
authors.initials: MA
authors.lastname: Webber
mesh_terms: D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D004926:Escherichia coli / Q000187:drug effects / Q000502:physiology; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D011550:Pseudomonas aeruginosa / Q000187:drug effects / Q000502:physiology; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics / Q000502:physiology*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000502:physiology
chemical_list: D026901:Membrane Transport Proteins
keywords: AcrAB-TolC; curli; efflux inhibitors