Synergistic bactericidal activity of Eremanthus erythropappus oil or beta-bisabolene with ampicillin against Staphylococcus aureus.

The activity of Eremanthus erythropappus oil (EO) and some of its compounds and their potential synergistic interaction with ampicillin against different strains of Staphylococcus aureus were investigated. Determination of chemical composition of EO by gas chromatography-mass spectrometry (GC/MS) and bioguided chemical fractionation led to the identification of beta-bisabolene as the main active compound. A synergistic bactericidal activity of EO or beta-bisabolene with ampicillin against Staphylococcus aureus was observed in a time-kill assay. EO and beta- bisabolene have the potential to restore the effectiveness of ampicillin against resistant S. aureus.