A-050. Mechanisms of Action of a Citrus Essential Oil Blend against Enterococcus spp

K. Fisher, C. Phillips;
Univ. of Northampton, Northampton, UNITED KINGDOM.

Background: Citrus essential oils have been recognised as antimicrobials since the 4th century and, in more recent years, have shown to be effective against not only yeast, moulds and spore forming bacteria but also food-poisoning bacteria including Enterococcus spp., reducing growing cultures by 5.5-10 log when used in both vapour and direct oil form. The mechanisms by which EOs bring about their antibacterial effect is incompletely understood. Enterococcus was previously considered harmless to humans however, in the last decade it has been reported as the second most common cause of wound and urinary tract infection and the third most common cause of bacteraemia. This investigation investigated the mechanisms by which a blend of orange (Citrus sinensis) : bergamot (Citrus bergamia) (1:1 v/v) in both vapour (9mg/l) and direct oil (2% v/v) form brings about its antimicrobial effect on E. faecium and E. faecalis. Methods: A NPN assay was used to demonstrate changes in cell membrane permeability. Intra and extracellular ATP concentrations were assessed using an assay based on luminescence and membrane potential and intracellular pH were measured using fluorescence assays using 3,3 dipropylthiacarbocyanine and carboxyfluorescein diacetate succinimidyl ester resepectively. Results: The permeability of the cell is increased by a factor of 2 after being subjected to direct oils and by x 40 after vapour contact. This is coupled with decreases of 1.5 in intracellular pH, 20 a.u. in membrane potential and 35 pmol/mg protein of intracellular ATP concentration. Conclusion: The citrus essential oil blend at low concentrations is affecting the cell membrane and therefore cell homeostasis, suggesting its possible use against a range of bacterial pathogens.