title: Assessment of three Resistance-Nodulation-Cell Division drug efflux transporters of Burkholderia cenocepacia in intrinsic antibiotic resistance.
abstract: BACKGROUND
  Burkholderia cenocepacia are opportunistic Gram-negative bacteria that can cause chronic pulmonary infections in patients with cystic fibrosis. These bacteria demonstrate a high-level of intrinsic antibiotic resistance to most clinically useful antibiotics complicating treatment. We previously identified 14 genes encoding putative Resistance-Nodulation-Cell Division (RND) efflux pumps in the genome of B. cenocepacia J2315, but the contribution of these pumps to the intrinsic drug resistance of this bacterium remains unclear.
  
  
  RESULTS
  To investigate the contribution of efflux pumps to intrinsic drug resistance of B. cenocepacia J2315, we deleted 3 operons encoding the putative RND transporters RND-1, RND-3, and RND-4 containing the genes BCAS0591-BCAS0593, BCAL1674-BCAL1676, and BCAL2822-BCAL2820. Each deletion included the genes encoding the RND transporter itself and those encoding predicted periplasmic proteins and outer membrane pores. In addition, the deletion of rnd-3 also included BCAL1672, encoding a putative TetR regulator. The B. cenocepacia rnd-3 and rnd-4 mutants demonstrated increased sensitivity to inhibitory compounds, suggesting an involvement of these proteins in drug resistance. Moreover, the rnd-3 and rnd-4 mutants demonstrated reduced accumulation of N-acyl homoserine lactones in the growth medium. In contrast, deletion of the rnd-1 operon had no detectable phenotypes under the conditions assayed.
  
  
  CONCLUSIONS
  Two of the three inactivated RND efflux pumps in B. cenocepacia J2315 contribute to the high level of intrinsic resistance of this strain to some antibiotics and other inhibitory compounds. Furthermore, these efflux systems also mediate accumulation in the growth medium of quorum sensing molecules that have been shown to contribute to infection. A systematic study of RND efflux systems in B. cenocepacia is required to provide a full picture of intrinsic antibiotic resistance in this opportunistic bacterium.
authors.affiliation: Department of Genetics and Microbiology, University of Pavia, Pavia, Italy. buroni.s@ipvgen.unipv.it
authors.forename: Silvia
authors.initials: S
authors.lastname: Buroni
authors.forename: Maria R
authors.initials: MR
authors.lastname: Pasca
authors.forename: Ronald S
authors.initials: RS
authors.lastname: Flannagan
authors.forename: Silvia
authors.initials: S
authors.lastname: Bazzini
authors.forename: Anna
authors.initials: A
authors.lastname: Milano
authors.forename: Iris
authors.initials: I
authors.lastname: Bertani
authors.forename: Vittorio
authors.initials: V
authors.lastname: Venturi
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Valvano
authors.forename: Giovanna
authors.initials: G
authors.lastname: Riccardi
mesh_terms: D054742:Acyl-Butyrolactones / Q000032:analysis; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D016956:Burkholderia cepacia / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism; D004269:DNA, Bacterial / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D005798:Genes, Bacterial; D026901:Membrane Transport Proteins / Q000235:genetics / Q000378:metabolism*; D008826:Microbial Sensitivity Tests; D016296:Mutagenesis; D015242:Ofloxacin / Q000378:metabolism; D009876:Operon; D053038:Quorum Sensing
chemical_list: D054742:Acyl-Butyrolactones; D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; D026901:Membrane Transport Proteins; D015242:Ofloxacin