title: Gene expression analysis of the SdeAB multidrug efflux pump in antibiotic-resistant clinical isolates of Serratia marcescens.
abstract: OBJECTIVE
  Many isolates of Serratia marcescens, a well-known opportunistic pathogen, can be multidrug resistant. Fluoroquinolones are among the most important groups of antibiotics used for treatment of these organisms. However, fluoroquinolone resistance among S. marcescens isolates is fast increasing. Drug extrusion through efflux pumps like SdeAB/ HasF is one of the major mechanisms of resistance to fluoroquinolones. This study was carried out to analyze, through gene expression analysis of sdeB, the relative contribution of this mechanism toward fluoroquinolone resistance in clinical isolates of Serratia.
  
  
  METHODS
  Total RNA from 45 clinical isolates of S. marcescens was isolated. Quantitative real-time RT PCR was performed on the extracted RNA to study the gene expression of sdeB and was normalized to the sdeB expression in the standard strain of S. marcescens.
  
  
  RESULTS
  Of the 45 isolates analyzed, sdeB expression was found to be elevated in 20 isolates (44%). Of these 20 isolates, eight (40%) were fully resistant to at least one of the fluoroquinolones studied. Conversely, of the 20 isolates that over-expressed sdeB, 12 (60%) were fully sensitive to all fluoroquinolones tested.
  
  
  CONCLUSIONS
  Drug efflux pumps are an important means of fluoroquinolone resistance among clinically important species of Serratia. The expression of these pumps can be up-regulated in the presence of antibiotics and have the potential for changing the phenotype from sensitive to resistant, thus contributing to therapeutic failures.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Manitoba, Winnipeg, MB, Canada.
authors.forename: S D
authors.initials: SD
authors.lastname: Dalvi
authors.forename: E A
authors.initials: EA
authors.lastname: Worobec
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology; D024901:Drug Resistance, Multiple, Bacterial; D024841:Fluoroquinolones / Q000378:metabolism / Q000494:pharmacology*; D020869:Gene Expression Profiling; D006801:Humans; D026901:Membrane Transport Proteins / Q000096:biosynthesis* / Q000235:genetics*; D060888:Real-Time Polymerase Chain Reaction; D016868:Serratia Infections / Q000382:microbiology; D012706:Serratia marcescens / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D024841:Fluoroquinolones; D026901:Membrane Transport Proteins