title: The mechanism of action of a citrus oil blend against Enterococcus faecium and Enterococcus faecalis.
abstract: OBJECTIVE
  The aim was to explore the mechanisms by which a blend of orange (Citrus sinensis) : bergamot (Citrus bergamia) (1 : 1 v/v) EO (essential oil) (2% v/v) and its vapour (15 mg l(-1) air) brings about its antimicrobial effect against Enterococcus faecium and Enterococcus faecalis.
  
  
  RESULTS
  Cells were exposed to the blend in oil or vapour form in a sealed unit. Membrane permeability was measured using an NPN assay and intra and extracellular ATP concentrations were assessed using luminescence. Assays using 3,3-dipropylthiacarbocyanine and carboxyfluorescein diacetate succinimidyl ester measured membrane potential and intracellular pH changes. TEM images of treated cells indicate morphological differences and show the possible uptake of the EO into the cell. After cells were exposed to EO or vapour, cell permeability increased by x2 and x40 respectively. A decrease of 1.5 in intracellular pH, 20 a.u. in membrane potential and 18 pmol mg(-1) protein of intracellular ATP occurred.
  
  
  CONCLUSIONS
  The EO blend affects the cell membrane and cell homeostasis resulting in inhibition of growth or cell death.
  
  
  CONCLUSIONS
  Understanding the mechanisms by which EOs bring about their antibacterial effect could lead to an alternative to chemical-based bactericides for use against Enterococcus sp.
authors.affiliation: University of Northampton, UK. katie.fisher@northampton.ac.uk
authors.forename: K
authors.initials: K
authors.lastname: Fisher
authors.forename: C
authors.initials: C
authors.lastname: Phillips
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D002463:Cell Membrane Permeability / Q000187:drug effects; D013293:Enterococcus faecalis / Q000187:drug effects* / Q000502:physiology; D016984:Enterococcus faecium / Q000187:drug effects* / Q000502:physiology; D005453:Fluorescence; D006863:Hydrogen-Ion Concentration; D008564:Membrane Potentials / Q000187:drug effects; D009822:Oils, Volatile / Q000378:metabolism / Q000494:pharmacology*; D010938:Plant Oils / Q000378:metabolism / Q000494:pharmacology*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000900:Anti-Bacterial Agents; D009822:Oils, Volatile; D010938:Plant Oils; C068336:bergamot oil; D000255:Adenosine Triphosphate; C087245:orange oil