Bactericidal effects and time-kill studies of the essential oil from the fruits of Zanthoxylum limonella on multi-drug resistant bacteria

Zanthoxylum limonella Alston is commonly used plant in Thailand for flavoring of foods and in traditional medicine. In this study, we investigated the crude essential oil, the distilled fractions thereof and the three pure major compounds of the oil from Z. limonella fruits for antibacterial activities against several bacteria including multi-drug resistant bacteria. The essential oil fractions I and II, and sabinene, the major compound of fractions I (54%) and II (41%), showed antibacterial activity against both Gram-positive and Gram-negative bacteria tested, except Pseudomonas aeruginosa. The crude oil showed higher antibacterial activity than sabinene against all tested bacteria, suggesting the presence of potent minor compound(s) with an additive effect, or less potent compound( s) with a synergistic effect among the components of the crude oil. The essential oil showed a potent killing effect, achieving a complete elimination of Staphylococcus aureus and Escherichia coli within a 9-minute exposure to a two-fold minimal bactericidal concentration level, while the multi-drug resistant bacteria, methicillin-resistant S. aureus and the extended-spectrum beta-lactamase-producing E. coli, were completely eradicated within 90 minutes at the same dose. This is the first report on the essential oil from Z. limonella fruits against multi-drug resistant bacteria. The essential oil has potential uses in food preservation and as an antiseptic for medical use.