title: Contribution of OqxAB efflux pumps to quinolone resistance in extended-spectrum-β-lactamase-producing Klebsiella pneumoniae.
abstract: OBJECTIVE
  The aims of this study were to analyse the presence of oqxA and oqxB genes in a collection of extended-spectrum β-lactamase (ESBL)-producing Klebsiella pneumoniae strains, to determine their chromosomal and/or plasmidic locations and to analyse expression levels in relation to susceptibility or resistance to quinolones.
  
  
  METHODS
  A collection of 114 non-repetitive isolates of ESBL-producing K. pneumoniae was used. K. pneumoniae ATCC 27799 and K. pneumoniae ATCC 700603 were also included. Detection of oqxA and oqxB genes was performed by PCR. Testing for chromosomal and/or plasmidic location was carried out using plasmid DNA and subsequent hybridization. oqxA gene expression was analysed using real-time RT-PCR. Transfer of the plasmid-encoded OqxAB was evaluated.
  
  
  RESULTS
  The prevalence of both oqxA and oqxB detected in K. pneumoniae was high: 76% and 75%, respectively. Hybridization assays showed that oqxA (16%) and oqxB (13%) were simultaneously present in locations on the chromosome and on large plasmids. The plasmids were transferable by transformation into K. pneumoniae. RT-PCR assays showed higher expression (4-fold) in strains with reduced susceptibility to quinolones than in susceptible strains. Interestingly, K. pneumoniae ATCC 700603 showed an 18-fold higher expression than K. pneumoniae ATCC 27799. These differences were in accordance with quinolone susceptibility.
  
  
  CONCLUSIONS
  The prevalence of the OqxAB efflux pump (both chromosomal and plasmid encoded) in ESBL-producing K. pneumoniae is high in Spain and represents a potential reservoir for the spread of these genes. High expression of this pump contributes to reduced susceptibility to quinolones in clinical isolates of ESBL-producing K. pneumoniae.
authors.affiliation: Department of Microbiology,  University of Seville, Seville,  Spain.
authors.forename: J M
authors.initials: JM
authors.lastname: Rodríguez-Martínez
authors.forename: P
authors.initials: P
authors.lastname: Díaz de Alba
authors.forename: A
authors.initials: A
authors.lastname: Briales
authors.forename: J
authors.initials: J
authors.lastname: Machuca
authors.forename: M
authors.initials: M
authors.lastname: Lossa
authors.forename: F
authors.initials: F
authors.lastname: Fernández-Cuenca
authors.forename: J
authors.initials: J
authors.lastname: Rodríguez Baño
authors.forename: L
authors.initials: L
authors.lastname: Martínez-Martínez
authors.forename: Á
authors.initials: Á
authors.lastname: Pascual
mesh_terms: D024881:Drug Resistance, Bacterial / Q000187:drug effects / Q000235:genetics*; D015964:Gene Expression Regulation, Bacterial; D006801:Humans; D007711:Klebsiella pneumoniae / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics*; D008826:Microbial Sensitivity Tests / Q000379:methods; D015363:Quinolones / Q000494:pharmacology*; D001618:beta-Lactamases / Q000096:biosynthesis / Q000235:genetics* / Q000302:isolation & purification
chemical_list: D015363:Quinolones; D001618:beta-Lactamases