title: Role of TolC in Klebsiella oxytoca resistance to antibiotics.
abstract: OBJECTIVE
  The Gram-negative human pathogen Klebsiella oxytoca is often resistant to several antibiotics such as fluoroquinolones, erythromycin, tetracycline, chloramphenicol and others. The aim of this study was to look at the mechanisms leading to this resistance and particularly the role of TolC and efflux mechanisms in determining resistance.
  
  
  METHODS
  Ciprofloxacin accumulation was measured spectrofluorometrically. Growth inhibition assays were performed in the presence or absence of carbonyl cyanide m-chlorophenylhydrazone (10 mg/L, final concentration). The genome of K. oxytoca was analysed for the existence of loci encoding tolC by PCR using primers for the Enterobacter aerogenes tolC gene and subsequently sequenced. A plasmid named pUC18TolC was constructed and inserted into Escherichia coli C600tolC,Tn5, and the function of TolC was analysed. The structure modelling was performed using the Modeller program.
  
  
  RESULTS
  The existence of the AcrAB efflux mechanism was demonstrated in the species, and a TolC-like protein, a channel-forming protein at the external membrane that allows the extrusion of antibiotics by the AcrAB efflux pump, was cloned, sequenced and a model proposed.
  
  
  CONCLUSIONS
  K. oxytoca express a functional TolC that lacks a fragment of six amino acids characteristic of the external loops of TolC in E. coli. This makes this species resistant to a few colicins.
authors.affiliation: Laboratory of Microbiology, Department of Pathology and Experimental Therapeutics, Medical and Dental Schools, University of Barcelona, Feixa Llarga s/n Hospitalet, 08907 Barcelona, Spain.
authors.forename: Anna
authors.initials: A
authors.lastname: Fenosa
authors.forename: Ester
authors.initials: E
authors.lastname: Fusté
authors.forename: Lidia
authors.initials: L
authors.lastname: Ruiz
authors.forename: Patricia
authors.initials: P
authors.lastname: Veiga-Crespo
authors.forename: Teresa
authors.initials: T
authors.lastname: Vinuesa
authors.forename: Victor
authors.initials: V
authors.lastname: Guallar
authors.forename: Tomas G
authors.initials: TG
authors.lastname: Villa
authors.forename: Miguel
authors.initials: M
authors.lastname: Viñas
mesh_terms: D000368:Aged; D000595:Amino Acid Sequence; D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology*; D001425:Bacterial Outer Membrane Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D002939:Ciprofloxacin / Q000378:metabolism; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D024881:Drug Resistance, Bacterial; D004926:Escherichia coli / Q000235:genetics; D006801:Humans; D041121:Klebsiella oxytoca / Q000187:drug effects* / Q000235:genetics*; D008297:Male; D008826:Microbial Sensitivity Tests; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D000900:Anti-Bacterial Agents; D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; D002939:Ciprofloxacin