Chemical Constituents and Antibacterial Activity of Essential Oil of Prangos ferulacea (L.) Lindl. Fruits

1. Intorduction

     Many infectious diseases have been treated with herbal remedies throughout the history of mankind. Even today, plant materials play a major role in primary health care as therapeutic remedies in many countries [1, 2]. Plants still continue to be an important source of drugs for majority of the world population [3-5]. The genus of Prangos with the common Persian name of "Jashir" include 15 species which are growing wildly in many regions of Iran. Some species are distributed in Anatolia, Central Asia and Caucasian. Five species delicated to Iran include: P. gaubae, P. calligonoides, P. cheilantifolia, P. tuberculata, and P. crossoptera which are distributed in the north and central provinces of Iran [6].

      Previous phytochemical studies on P. ferulacea (L.) Lindl. have indicated the presence of coumarin and its derivatives [7, 8]. The fruits of endemic P. unchtritzii Boiss. and Hausskn. (Apiaceae) are subjected to hydrodistillation and microdistillation. The resulting volatiles were investigated by gas chromatography-mass spectrometery (GC-MS) to determine the composition of the essential oil and 109 compounds representing 86.7% and thirty two compounds representing 90.0% were identified and isolated by two different techniques, respectively. Column chromatography of the essential oil yielded a new bisabolene ethe (7-epi-1,2-dehydro sesquicineole), which was characterized by spectral methods (GC- FTIR- 1D-, 2D NMR and HRESIMS) [9].

    The water distilled essential oil from crushed dry fruits of P. heyniae, a recently described endemic in Turkey, collected from two localities were analyzed by GC/MS and 61 and 79 compounds representing 92.2%, 89.8% of the oils were characterized with β-bisabolenal (53.3% and 18.0%), β-bisabolene (14.6% and 2.3%) and β-bisabolene (12.1% and 10.1%) as the main constituents [10].

     The present study reports the composition of the essential oils isolated from the dried fruits of P. ferulacea by GC and GC/MS. The antimicrobial activities of the essential oil against some gram positive and gram negative bacteria were also investigated.

Table 1. The essential oil Prangos ferulacea fruits' essential oil.

^aRI: Retention indices as determined on a DB-5 column using the homologous series of n-alkanes (C_{8- 24}).

Table 2. Antimicrobial activity of Prango ferulacea fruits’ essential oil using disk diffusion assay.

2. Materials and methods

2.1. Plant material

     Fresh plants of P. ferulacea with fruits and roots collected in May and June 2006 from Tehran (Tehran province): between Shemshak and Dizin, 30°02'30"N, 51°27'41"E, 2500 m, the plant was identified by Yousef Ajani and a voucher specimen (2055) was deposited at the herbarium of Tehran University of Medical Sciences.

2.2. Isolation of the essential oil

     The dried fruits were submitted to water distillation for 4 h using a Clevenger type apparatus. The obtained essential oil (yield 1.50% v/w) were dried over anhydrous sodium sulfate and stored at +4 °C until GC/MS analysis.

2.3. Antimicrobial activity

     The disk diffusion assay [11] was used to determine the growth inhibition of bacteria by the essential oil. The following bacteria were used: Staphylococus aureus ATCC 29737, S. epidermis ATCC 14990, Bacillus subtili ATCC 6633, Eschrechia coli ATCC 8739 and Pseudomonas aeroginosa ATCC 9027. The bacteria were obtained from department of Drug and Food Control, Faculty of Pharmacy, Tehran University of Medical Sciences.

     Base plates were prepared by pouring 10 ml Mueller-Hinton (MH) agar into sterile Petri dishes (9 cm) and allowed to set. Mueller- Hinton agar held at 80 °C was incubated with a broth cultured (1×10⁸ cfu/ml) of the test organism and poured over the base plates forming a homogenous top layers. Aliquots of 2.5 μl [2 mg, (d= 0.8)] of plant essential oil were applied on filter paper disc. Discs were placed on to the second top layer of the agar plates. The essential oil was tested in quadruplicate (4 disc/plate) with neomycin (200 μg) per disc as reference or positive control. The plates were evaluated after incubation at 37° C for 18 h. Antibacterial activity was expressed as the inhibition zone (mm) was produced [12]. The activity of neomycin was introduced in this equation to adjust for plate-to-plate variation in the sensitivity of particular bacterial strain. Minimum inhibition of concentration (MICs) of the essential oil was determined against the tested microorganisms. The agar dilution method [13] was used for S. aureus, S. epidermis, B. subtilis, E. coli, P. aeroginosa with two full serial dilutions of plant essential oil from to 0.5 mg/ ml of medium.

    DMSO was used as the solvent for mixing essential oil with the medium. MIC was taken as the lowest concentration of the essential oil which completely inhibited bacterial growth after 18 h of incubation at 37 °C. Neomycin and DMSO with no essential oil were used as the positive and negative controls, respectively.

2.4. GC/MS analysis

     Analysis of the essential oil was performed using a Hewlett Packard 6890 GC equipped with a HP-5MS capillary column (30 m×0.22 mm i.d., 0.25 μm film thickness) and a mass spectrophotometer 5973 from the same company for GC/MS detection with an electron ionization system energy (10 eV) was used. Helium was the carrier gas, at a flow rate of 1 ml/min., injector and detector MS transfer line temperature were set at 250 and 290 °C, respectively. Column temperature was initially kept at 60 °C for 5 min., then gradually increased to 220 °C at the rate of 6 °C/min. Identification of the essential oil components was based on comparisons of their mass spectra with those of Wiley library data of MS and the literature data as well as on comparison of their retention indices with normal alkanes (C₈-C₂₄).

Table 3. The minimum inhibitory concentration of Prangos ferulacea fruits’ essebtial oil against some Gram- positive and Gramnegative bacteria.

3. Results and discussion

     The composition of P. ferulacea fruits essential oil (Table 1) was consist of 39 compounds; 11 of them accounting for 85.25% of the total oil. The most important compounds were monoterpene (more than 85%). The major components were chrysantenyl acetate (26.53%), limonene (19.59%), α-pinene (19.50%), α-humulene (2.84%).

     The essential oil was tested against five standard bacterial strains (gram positive and gram negative). The MIC values (0.5×10^-3-12.5×10^-3 mg/ ml) of the essential oil for the sensitive bacteria are represented in Table 3.

     In summary, the data summarized in Table 3 indicate that the essential oil of P. ferulacea fruits have antibacterial activity against both gram positive and gram negative bacteria, which may justify the use of these species in traditional medicine, and underline the importance of the bioactive ethnobotanical approach for the selection of plants for the discovery of the new antibacterial substances. Some compounds of this essential oil such as limonen, α-pinene and α-humulene have been reported to possess antibacterial activity [14].

Acknowledgements

     This research was supported by Tehran University of Medical Sciences and Health Services grant. The authors are grateful to Y. Ajani for collection and identification of plants and Dr. Sereshti for GC operation.