title: Identification of efflux pump-mediated multidrug-resistant bacteria by the ethidium bromide-agar cartwheel method.
abstract: OBJECTIVE
  Bacterial multidrug resistance may be mediated by the overexpression of efflux pumps. Conventional evaluation of efflux activity using efflux pump substrates, such as ethidium bromide, requires specialised instrumentation. The agar-based method, previously reported, has been modified to evaluate as many as twelve bacterial strains and has been termed the ethidium bromide-agar cartwheel method.
  
  
  METHODS
  Agar plates containing different concentrations of ethidium bromide were swabbed with bacterial cultures. The cell efflux capacity increased with increasing ethidium bromide concentration, which produced fluorescence of the bacterial mass.
  
  
  RESULTS
  The method was shown to be useful for the detection of efflux activity among multidrug-resistant Gram-negative and Gram-positive clinical isolates, as confirmed by the determination of minimum inhibitory concentration for several antibiotics in the presence of known efflux pump inhibitors.
  
  
  CONCLUSIONS
  This method may be adapted to the clinical laboratory for the presumptive identification of multidrug-resistant isolates that overexpress efflux pump systems.
authors.affiliation: Unit of Mycobacteriology and UPMM, Instituto de Higiene e Medicina Tropical, Universidade Nova de Lisboa (IHMT/UNL), Rua da Junqueira, 100, 1349-008 Lisbon, Portugal.
authors.forename: Marta
authors.initials: M
authors.lastname: Martins
authors.forename: Miguel
authors.initials: M
authors.lastname: Viveiros
authors.forename: Isabel
authors.initials: I
authors.lastname: Couto
authors.forename: Sofia S
authors.initials: SS
authors.lastname: Costa
authors.forename: Teresa
authors.initials: T
authors.lastname: Pacheco
authors.forename: Séamus
authors.initials: S
authors.lastname: Fanning
authors.forename: Jean-Marie
authors.initials: JM
authors.lastname: Pagès
authors.forename: Leonard
authors.initials: L
authors.lastname: Amaral
mesh_terms: D000362:Agar; D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001419:Bacteria / Q000187:drug effects / Q000302:isolation & purification* / Q000378:metabolism*; D001424:Bacterial Infections / Q000188:drug therapy / Q000382:microbiology; D001431:Bacteriological Techniques / Q000295:instrumentation / Q000379:methods; D001692:Biological Transport / Q000187:drug effects; D024901:Drug Resistance, Multiple, Bacterial; D004996:Ethidium / Q000378:metabolism* / Q000493:pharmacokinetics; D006090:Gram-Negative Bacteria / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism; D006094:Gram-Positive Bacteria / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism; D006801:Humans; D008826:Microbial Sensitivity Tests; D015203:Reproducibility of Results
chemical_list: D000900:Anti-Bacterial Agents; D000362:Agar; D004996:Ethidium