title: Antibacterial activity and mode of action of tert-butylhydroquinone (TBHQ) and its oxidation product, tert-butylbenzoquinone (TBBQ).
abstract: OBJECTIVE
  The antioxidant tert-butylhydroquinone (TBHQ) is a food additive reported to have antibacterial activity, and may therefore have application in the healthcare setting. This study sought to characterize the antibacterial activity and mode of action of TBHQ and its oxidation product, tert-butylbenzoquinone (TBBQ).
  
  
  METHODS
  The stability of TBHQ/TBBQ was studied in buffer. Susceptibility testing was performed by broth microdilution, and killing and lytic activity were evaluated by viable counting and culture turbidity measurements. Mode of action studies included following the incorporation of radiolabelled precursors into macromolecules. The effect of TBHQ/TBBQ upon bacterial and mammalian membranes was assessed using the BacLight(TM) assay and by monitoring the haemolysis of equine erythrocytes.
  
  
  RESULTS
  TBHQ underwent oxidation in solution to form TBBQ. When oxidation was prevented, TBHQ lacked useful antibacterial activity, indicating that TBBQ is responsible for the antibacterial activity attributed to TBHQ. TBBQ demonstrated activity against Staphylococcus aureus SH1000 (MIC 8 mg/L) and against a panel of clinical S. aureus isolates (MIC90 16 mg/L). TBBQ at 4× MIC caused a >4 log10 drop in cell viability within 6 h without lysis, and eradicated staphylococcal biofilms at 8× MIC. TBBQ did not display preferential inhibition of any single macromolecular synthetic pathway, but caused loss of staphylococcal membrane integrity without haemolytic activity.
  
  
  CONCLUSIONS
  TBBQ is responsible for the antibacterial activity previously ascribed to TBHQ. TBBQ prompts loss of staphylococcal membrane integrity; it is rapidly and extensively bactericidal, but is non-lytic. In view of the potent and selective bactericidal activity of TBBQ, this compound warrants further investigation as a candidate antistaphylococcal agent.
authors: Antimicrobial Research Centre and School of Molecular and Cellular Biology, University of Leeds, Leeds, UK.
authors: N
authors: N
authors: Ooi
authors: I
authors: I
authors: Chopra
authors: A
authors: A
authors: Eady
authors: J
authors: J
authors: Cove
authors: R
authors: R
authors: Bojar
authors: A J
authors: AJ
authors: O'Neill
mesh_terms: D000818:Animals; D000900:Anti-Bacterial Agents / Q000737:chemistry / Q000494:pharmacology*; D001419:Bacteria / Q000187:drug effects*; D001426:Bacterial Proteins / Q000096:biosynthesis; D018441:Biofilms / Q000187:drug effects; D003470:Culture Media; D004269:DNA, Bacterial / Q000096:biosynthesis; D004355:Drug Stability; D004912:Erythrocytes / Q000187:drug effects; D006736:Horses; D006873:Hydroquinones / Q000737:chemistry / Q000494:pharmacology*; D008826:Microbial Sensitivity Tests; D010084:Oxidation-Reduction; D012329:RNA, Bacterial / Q000096:biosynthesis
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D003470:Culture Media; D004269:DNA, Bacterial; D006873:Hydroquinones; D012329:RNA, Bacterial; C018855:2-tert-butylhydroquinone
keywords: Staphylococcus aureus; antioxidants; biofilms; haemolysis; membrane integrity