title: TolC dependency of multidrug efflux systems in Salmonella enterica serovar Typhimurium.
abstract: OBJECTIVE
  TolC is a major outer membrane channel and it plays an important role in the excretion of a wide range of molecules, including antibiotics. A recent study has shown that Salmonella enterica serovar Typhimurium has nine functional drug efflux pumps; however, the TolC dependency of these efflux pumps remains to be studied in detail. The aim of this study was to investigate the TolC dependency of multidrug efflux pumps in this organism.
  
  
  METHODS
  All genes encoding the drug efflux systems were cloned into the pUC118 vector. Constructed plasmids were transformed into DeltaacrB and DeltatolC mutants of S. enterica serovar Typhimurium ATCC 14028s, and then the drug susceptibilities of these transformants were determined.
  
  
  RESULTS
  Plasmids carrying the acrAB, acrD, acrEF, mdsAB, mdtABC, emrAB or macAB genes did not confer resistance to the tolC mutant, whereas they conferred drug resistance to the acrB mutant. Only three plasmids carrying mdsABC, mdfA or mdtK conferred resistance to the tolC mutant.
  
  
  CONCLUSIONS
  TolC is required for the function of seven drug efflux systems (AcrAB, AcrD, AcrEF, MdsAB, MdtABC, EmrAB and MacAB) in S. enterica serovar Typhimurium.
authors.affiliation: Laboratory of Microbiology and Infectious Diseases, Institute of Scientific and Industrial Research, Osaka University, 8-1 Mihogaoka, Ibaraki, Osaka 567-0047, Japan.
authors.forename: Tsukasa
authors.initials: T
authors.lastname: Horiyama
authors.forename: Akihito
authors.initials: A
authors.lastname: Yamaguchi
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Nishino
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics* / Q000378:metabolism*; D024901:Drug Resistance, Multiple, Bacterial; D006801:Humans; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D008954:Models, Biological; D008958:Models, Molecular; D012486:Salmonella typhimurium / Q000235:genetics* / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D026901:Membrane Transport Proteins