title: Effects of natural mutations in the ramRA locus on invasiveness of epidemic fluoroquinolone-resistant Salmonella enterica serovar Typhimurium isolates.
abstract: BACKGROUND
  Fluoroquinolone (FQ) resistance is increasing worldwide among Salmonella species. Among the mechanisms involved, increased efflux via the tripartite AcrAB-TolC efflux system is mainly modulated through control of expression via the ramRA regulatory locus gene products. Interestingly, in some reference strains these have also been experimentally shown to regulate cell invasion-related genes of the type III secretion system 1 (T3SS-1). In this study, we investigated whether natural mutations occurring in this locus in FQ-resistant S. enterica serovar Typhimurium epidemic clones resulted in the same effects.
  
  
  METHODS
  Quantitative reverse transcription polymerase chain reaction and cell invasion assays were used to study 3 clinical FQ-resistant S. Typhimurium isolates representative of the DT104 and DT204 epidemic clones. For comparison, 3 control reference quinolone-susceptible strains were included.
  
  
  RESULTS
  As previously shown, the investigated mutations altering RamR or its DNA-binding site increased expression of efflux genes dependently on ramA. However, the decreased expression of T3SS-1 genes previously reported was not always observed and seemed to be dependent on the genetic background of the FQ-resistant isolate. Indeed, a ramA-dependent decreased invasion of intestinal epithelial cells was only observed for a particular clinical ramR mutant.
  
  
  CONCLUSIONS
  ramRA mutations occurring in clinical FQ-resistant S. Typhimurium isolates may negatively modulate their invasiveness but this is strain-dependent.
authors.affiliation: INRA, UMR1282 Infectiologie et Santé Publique, Nouzilly, France. etienne.giraud@tours.inra.fr
authors.forename: Etienne
authors.initials: E
authors.lastname: Giraud
authors.forename: Sylvie
authors.initials: S
authors.lastname: Baucheron
authors.forename: Isabelle
authors.initials: I
authors.lastname: Virlogeux-Payant
authors.forename: Kunihiko
authors.initials: K
authors.lastname: Nishino
authors.forename: Axel
authors.initials: A
authors.lastname: Cloeckaert
mesh_terms: D001426:Bacterial Proteins / Q000235:genetics* / Q000378:metabolism; D024881:Drug Resistance, Bacterial; D004847:Epithelial Cells / Q000382:microbiology; D024841:Fluoroquinolones / Q000494:pharmacology*; D020869:Gene Expression Profiling; D006801:Humans; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000235:genetics* / Q000378:metabolism; D050505:Mutant Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D060888:Real-Time Polymerase Chain Reaction; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism; D012480:Salmonella Infections / Q000453:epidemiology / Q000382:microbiology; D012486:Salmonella typhimurium / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity*; D015534:Trans-Activators / Q000235:genetics* / Q000378:metabolism; D014774:Virulence; D037521:Virulence Factors / Q000235:genetics* / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D024841:Fluoroquinolones; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D050505:Mutant Proteins; D012097:Repressor Proteins; D015534:Trans-Activators; D037521:Virulence Factors; C579436:RamA protein, Salmonella enterica; C531999:RamA protein, Salmonella typhimurium