title: Genetic inactivation of acrAB or inhibition of efflux induces expression of ramA.
abstract: OBJECTIVE
  The transcriptional activator RamA regulates production of the multidrug resistance efflux AcrAB-TolC system in several Enterobacteriaceae. This study investigated factors that lead to increased expression of ramA.
  
  
  METHODS
  In order to monitor changes in ramA expression, the promoter region of ramA was fused to a gfp gene encoding an unstable green fluorescence protein (GFP) on the reporter plasmid, pMW82. The ramA reporter plasmid was transformed into Salmonella Typhimurium SL1344 and a ΔacrB mutant. The response of the reporter to subinhibitory concentrations of antibiotics, dyes, biocides, psychotropic agents and efflux inhibitors was measured during growth over a 5 h time period.
  
  
  RESULTS
  Our data revealed that the expression of ramA was increased in a ΔacrB mutant and also in the presence of the efflux inhibitors phenylalanine-arginine-β-naphthylamide, carbonyl cyanide m-chlorophenylhydrazone and 1-(1-naphthylmethyl)-piperazine. The phenothiazines chlorpromazine and thioridazine also increased ramA expression, triggering the greatest increase in GFP expression. However, inducers of Escherichia coli marA and soxS and 12 of 17 tested antibiotic substrates of AcrAB-TolC did not induce ramA expression.
  
  
  CONCLUSIONS
  This study shows that expression of ramA is not induced by most substrates of the AcrAB-TolC efflux system, but is increased by mutational inactivation of acrB or when efflux is inhibited.
authors.affiliation: Antimicrobials Research Group, School of Immunity and Infection, Institute of Microbiology and Infection, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK.
authors.forename: A J
authors.initials: AJ
authors.lastname: Lawler
authors.forename: V
authors.initials: V
authors.lastname: Ricci
authors.forename: S J W
authors.initials: SJ
authors.lastname: Busby
authors.forename: L J V
authors.initials: LJ
authors.lastname: Piddock
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism; D019677:Artificial Gene Fusion; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins / Q000032:analysis / Q000235:genetics; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000096:biosynthesis* / Q000235:genetics; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D015534:Trans-Activators / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002352:Carrier Proteins; D049452:Green Fluorescent Proteins; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D015534:Trans-Activators; C493251:AcrAB-TolC protein, Salmonella enterica; C531999:RamA protein, Salmonella typhimurium
keywords: antibiotic resistance; efflux inhibitors; phenothiazines