title: Differential impact of ramRA mutations on both ramA transcription and decreased antimicrobial susceptibility in Salmonella Typhimurium.
abstract: OBJECTIVE
  This study was focused on analysing the heterogeneity of mutations occurring in the regulators of efflux-mediated MDR in Salmonella Typhimurium. Moreover, the impact of such mutations on impairing the transcription of ramA, acrB, tolC and acrF was also assessed as was the impact on the resistance or decreased susceptibility phenotype.
  
  
  METHODS
  Strains were selected in vitro under increasing ciprofloxacin concentrations. Etest and broth microdilution tests were used to determine the MICs of several unrelated compounds. Screening of mutations in the quinolone target genes and MDR regulators was performed. RT-PCR analysis was used to detect the levels of expression of acrB, tolC, ompF, acrF, emrB, acrR, ramA, soxS and marA.
  
  
  RESULTS
  All mutant strains showed increased MICs of most of the antimicrobials tested, with the exception of kanamycin. Mutations in the quinolone target genes did not occur in all the mutants, which all harboured mutations in the ramRA regulatory region. All the mutants overexpressed ramA, tolC and acrB (only tested in 60-wt derivatives), whereas differential results were seen for the remaining genes.
  
  
  CONCLUSIONS
  Mutations in the ramRA region related to resistance and/or decreased susceptibility to antimicrobials predominate in Salmonella. There is heterogeneity in the types of mutations, with deletions affecting RamR-binding sites having a greater impact on ramA expression and the MDR phenotype.
authors.affiliation: ISGlobal, Barcelona Ctr. Int. Health Res. (CRESIB), Hospital Clínic-Universitat de Barcelona, Barcelona, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Fàbrega
authors.affiliation: ISGlobal, Barcelona Ctr. Int. Health Res. (CRESIB), Hospital Clínic-Universitat de Barcelona, Barcelona, Spain.
authors.forename: Clara
authors.initials: C
authors.lastname: Ballesté-Delpierre
authors.affiliation: ISGlobal, Barcelona Ctr. Int. Health Res. (CRESIB), Hospital Clínic-Universitat de Barcelona, Barcelona, Spain Department of Clinical Microbiology, Hospital Clínic, School of Medicine, University of Barcelona, Barcelona, Spain jvila@ub.edu.
authors.forename: Jordi
authors.initials: J
authors.lastname: Vila
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D002939:Ciprofloxacin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D020869:Gene Expression Profiling; D006801:Humans; D008826:Microbial Sensitivity Tests; D027425:ATP-Binding Cassette, Sub-Family C Proteins / Q000096:biosynthesis* / Q000235:genetics; D009154:Mutation; D060888:Real-Time Polymerase Chain Reaction; D012486:Salmonella typhimurium / Q000187:drug effects* / Q000235:genetics; D015534:Trans-Activators / Q000096:biosynthesis* / Q000235:genetics; D014158:Transcription, Genetic
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D002939:Ciprofloxacin; D027425:ATP-Binding Cassette, Sub-Family C Proteins; D015534:Trans-Activators; C531999:RamA protein, Salmonella typhimurium; C000596674:RamR protein, Salmonella typhimurium