title: Antibacterial and resistance-modifying activities of thymoquinone against oral pathogens.
abstract: BACKGROUND
  The presence of resistant bacteria in the oral cavity can be the major cause of dental antibiotic prophylaxis failure. Multidrug efflux has been described for many organisms, including bacteria and fungi as part of their drugs resistance strategy. The discovery of a new efflux pump inhibitor could extend the useful lifetime of some antibiotics.
  
  
  METHODS
  In this study, the MICs of thymoquinone (TQ), tetracycline and benzalkonium chloride (BC) were determined in absence and in presence of a sub-MIC doses of thymoquinone (1/2 MIC). In addition the 4,6-diamidino-2-phenylindole (DAPI) efflux assay was carried out to determine the effect of TQ on DAPI cells accumulation.
  
  
  RESULTS
  TQ induced a selective antimicrobial activity. Its synergic effect resulted in at least a 4-fold potentiation of the tested antibiotics and antiseptic. In addition, TQ inhibited the DAPI efflux activity in a concentration-dependent manner. The rate of DAPI accumulation in clinical isolates was enhanced with TQ (0 to 200 μg/ml). There is also a decrease in loss of DAPI from bacteria in the presence of TQ. The concentration causing 50% of DAPI efflux inhibition after 15 minutes was approximately 59 μg/ml for Pseudomonas aeroginosa and 100 μg/ml and Staphylococcus aureus respectively.
  
  
  CONCLUSIONS
  TQ possesses a selective antibacterial activity against oral bacteria. It is therefore suggested that TQ could be used as a source of natural products with resistance-modifying activity. Further investigation is needed to assess their clinical relevance.
authors.affiliation: Laboratory of Analyses, Treatments and Valorisation of Environmental Wastes and Products, Faculty of Pharmacy, Monastir University, Avicenne Street 5000, Monastir, Tunisia. bochrak@yahoo.fr
authors.forename: Bochra
authors.initials: B
authors.lastname: Kouidhi
authors.forename: Tarek
authors.initials: T
authors.lastname: Zmantar
authors.forename: Hanene
authors.initials: H
authors.lastname: Jrah
authors.forename: Yosra
authors.initials: Y
authors.lastname: Souiden
authors.forename: Kamel
authors.initials: K
authors.lastname: Chaieb
authors.forename: Kacem
authors.initials: K
authors.lastname: Mahdouani
authors.forename: Amina
authors.initials: A
authors.lastname: Bakhrouf
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D001424:Bacterial Infections / Q000382:microbiology; D016227:Benzoquinones / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests; D009055:Mouth / Q000382:microbiology; D009059:Mouth Diseases / Q000382:microbiology*
chemical_list: D000900:Anti-Bacterial Agents; D016227:Benzoquinones; C003466:thymoquinone