In vitro inhibition of vancomycin-susceptible and vancomycin-resistant Enterococcus faecium and E. faecalis in the presence of citrus essential oils.

Glycopeptide-resistant Enterococcus (GRE) is an important healthcare-acquired infection (HCAI) which costs the healthcare service many millions of pounds worldwide. In this study, lemon (Citrus limon), sweet orange (Citrus sinensis) or bergamot (Citrus bergamia) essential oils (EO) and their vapours, alone and in combination, are tested for their antimicrobial activity against vancomycin-resistant and vancomycin-sensitive strains of E. faecium and E. faecalis. A blend of 1:1 (v/v) orange and bergamot EO was the most effective of the oils and/or blends tested with a minimum inhibitory concentration (MIC), at 25 degrees C and pH 5.5, of 0.25-0.5% (v/v) and a minimum inhibitory dose (MID) of 50 mg/L, at 50 degrees C at pH 7.5, when viable counts reduced by 5.5-10 log10 colony forming units (cfu)/mL, suggesting that this blend of citrus oils is effective under a range of conditions for inhibiting the growth and survival of E. faecalis, E. faecium and VRE.