Chemical Composition and Antibacterial Activity of Essential Oils from Ferula L. Species against Methicillin-Resistant Staphylococcus aureus

Abstract

Essential oils (EOs) were obtained by hydrodistillation of various parts of Ferula ovina (Boiss.) Boiss., Ferula iliensis Krasn. ex. Korovin, and Ferula akitschkensis B. Fedtsch. ex Koso-Pol., collected in the flowering/budding and fruiting stages. Eight samples of EOs isolated from F. ovina and four samples from F. akitsckensis were analyzed by gas chromatography⁻mass spectrometry (GC-MS). The major constituents of F. ovina EOs were α-pinene (6.9⁻47.8%), β-pinene (1.5⁻7.1%), sabinene (0.1⁻20.5%), β-phellandrene (0⁻6.5%), trans-verbenol (0.9⁻7.4%), eremophilene (3.1⁻12%), and 6Z-2,5,5,10-tetramethyl-undeca-2,6,9-trien-8-one (0⁻13.7%). The major constituents of F. akitsckensis EOs were α-pinene (0⁻46.2%), β-pinene (0⁻47.9%), sabinene (0⁻28.3%), eremophilene (0⁻10.6), β-caryophyllene (0⁻7.5%), himachalen-7-ol (0⁻28.2%), and an himachalol derivative (0⁻8.3%). Samples of EOs from F. ovina, F. iliensis, and F. akitsckensis were evaluated for antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA) pulse-field gel electrophoresis type USA300 (LAC). EOs from F. ovina exhibited the highest antibacterial activity compared to samples from other Ferula spp., with the most potent EOs being isolated from roots at the flowering and fruiting stages and stems at the fruiting stage (IC₅₀ values of 19.1, 20.9, and 22.9 µg/mL, respectively). Although EOs demonstrated concentration-dependent inhibition of MRSA growth, analysis of the major constituents (α-pinene, β-pinene, and sabinene) showed that they had low activity, suggesting that other components were likely responsible for the observed bioactivity of the unfractionated EOs. Indeed, correlation of the GC-MS data with antibacterial activity suggested that the putative components responsible for antibacterial activity were, either individually or in combination, eremophilene and trans-verbenol. Overall, these results suggest that the EOs from F. ovina could have potential for use as alternative remedies for the treatment of infectious diseases caused by MRSA.

Keywords: Ferula; antibacterial activity; essential oil; methicillin-resistant Staphylococcus aureus (MRSA).

Figure 1

Ferula ovina essential oils (EOs) and their constituents inhibit MRSA growth in a dose-dependent manner. MRSA strain LAC USA300 was grown to mid exponential phase then resuspended in TSB (2 × 10⁵ CFU) and incubated with varied concentrations of EOs or constituents. CFUs were recovered following a 1 h incubation with the indicated concentrations of F. ovina EOs from roots at flowering (FOEO_Rfl) and fruiting (FOEO_Rfr) stages Panel (A) or EO constituents (±)-α-pinene and (−)-β-pinene Panel (B). * p < 0.001, as determined by one-way ANOVA with Dunnett’s test compared to LAC grown in DMSO. Data are from three separate experiments.

Figure 2

Plots of antibacterial activity versus the concentrations of eremophilene Panel (A), trans-verbenol Panel (B), and total sesquiterpene hydrocarbons Panel (C) in the EOs based on GC-MS data. Activities are represented as inverse (1/IC₅₀) values to account for the four inactive EO samples from F. akitschkensis. These samples, indicated as closed circles, were omitted from the regression calculation and are shown as outliers. Dashed lines indicate area of the 95% confidence band. FAEO_Lb, EO isolated from F. akitsckensis leaves at the budding stage; FOEO_Sfl, EO isolated from F. ovina stems at the flowering stage.