Abstract: The aerial parts of Salvia verbenaca L. (Labiatae) afforded an essential oil on steam distillation was analyzed by gas chromatography-mass spectrometry (GC/MS) using direct injection. Out of fifty-two peaks (representing 99.2% of the oil), forty-one components were identified representing 96.3% of the total oil composition. The major components were sabinene (16.0%), δ-cadinene (7.9%), a-pinene (7.3%), 4-terpeniol (7.4%) and limonene (6.7%). The oil was also screened for its anti-microbial activity, which exhibited a significant anti-bacterial activity against Bacillus subtilis, Staphylococcus aureus and Mycobacterium smegmatis, and a marked anti-fungal activity against Candida albicans.
Introduction
Salvia verbenaca L. (Labiatae) is widely distributed in tropical regions including Saudi Arabia. The alcoholic extract of the aerial parts has been reported to potentiate smooth muscle contractions induced by acetylcholine, histamine, BaCl2, and serotonin (Todorov et al., 1984). Previous reports on the plant have shown the presence of abietane diterpene quinone namely 6β-hydroxy-7α-acetoxy royleanone (Sabri et al., 1989) and 5-hydroxy 7, 4’-methoxy flavone (Camarasa et al., 1982) from the leaves of the plant. The literature survey revealed that no phytochemical and pharmacological work has been done so far on the essential oil of the aerial parts of the plant. We report herein the composition and anti-microbial activity of the essential oil, wherein forty-one components were identified by gas chromatography-mass spectrometry (GC/MS) using direct injection (Table 1). The anti-microbial activity was screened against Bacillus subtilis, Staphylococcus aureus, Mycobacterium smegmatis, Escherichia coli, Pseudomonas aeruginosa and Candida albicans (Table 2).
Materials and Methods
Plant material: The aerial parts of Salvia verbenaca L. were collected on 18th February 2001 from Fifa mountains, 18 Km south of Sabia city, Southern Province, Saudi Arabia. The taxonomist of the center, Dr. Atiqur-Rehman identified the plant, and a voucher specimen No. 14182 has been deposited at the herbarium, College of Pharmacy, King Saud University, for future reference.
Analysis of the essential oil: Fresh aerial parts (500gm) were crushed to coarse powder and steam distilled in a Clevenger apparatus for about four hours to obtain the yellow coloured oil (0.6 ml, 0.12% v/w), which was subjected to analysis by GC/MS using direct injection in the split mode under the following conditions:
Hewlett-Packard 5973 MSD GC/MS equipped with a quartz capillary column: 30 x 0.32 mm x 1.0 μ Rtx- 5 sil MS (Restek); oven temperature: 40 °C (hold 3 min) to 200 °C at 8 °C/ min then to 320 °C at 6 °C/min (hold 4 min); Injector temperature: 320 °C; Sample size: 0.2 μ L, split 1: 100; mass range: 39- 500 amu, 3.17 scans /sec; carrier gas: He; ionization energy: 70 eV. The qualitative identification of different constituents was performed by comparison of their retention times and mass spectra with those of the library.
Pharmacological screening: The anti-microbial activity was tested according to the National Committee of Clinical Laboratory Standards using American type of Culture Collection (ATCC) standard (Ferraro et al., 2000) against various microorganisms namely: Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Mycobacterium smegmatis and Candida albicans. The positive antibacterial and antifungal activities were established by the presence of measurable zones of inhibition after 24 hrs incubation for Bacillus subtilis and Staphylococcus aureus, and 48 hrs for Mycobacterium smegmatis and Candida albicans.
Results and Discussion
The results of the analysis of the essential oil are qualitative and semi-quantitative. The fresh aerial parts of Salvia verbenaca yielded 0.12% v/w of essential oil. The constituents identified by GC/MS analysis, their retention times and area percentages are summarized in Table 1. Out of fifty-two peaks (representing 99.2% of the oil), forty-one components were identified representing 96.3% of the total oil composition. Monoterpenes hydrocarbons were the major constituents in the oil. In addition to Sabinene (16.0%), that was the major monoterpene hydrocarbon, 4-terpeniol (7.4%), α- pinene (7.3%), limonene (6.7%) and δ-3-carene (4.0%) were present in fairly good amount.
On the other hand, α-cadinene (7.9%) was the major sesquiterpene hydrocarbon present in the oil. Other sesquiterpene hydrocarbons such as β-caryophyllene (5.0%) and β-elemene (3.4%) were also detected in appreciable amounts. Moreover, some minor components were also detected of which camphene (1.5%), δ-guaiene (1.2%), germacrene (1.1%) and β-selinene (0.8%) were identified.
The oil showed a significant anti-microbial potential on various microorganisms tested. The minimum inhibitory concentration (MIC) of the oil was 2.0 mg/ml against Bacillus subtilis and Staphylococcus aureus, and 3.0 mg/ml against Mycobacterium smegmatis. In addition, the minimum inhibitory concentration against the fungus Candida albicans was 2.0 mg/ml. Other microorganisms that were tested such as Escherichia coli and Pseudomonas aeruginosa were resistant to the oil (Table 2).
| Table 1: | Identified chemical constituents in the essential oil of Salvia verbenaca |
| Table 2: | Antimicrobial activity of the essential oil of Salvia verbenaca |
| *Minimum inhibitory concentration (MIC) | |
The above results indicate that the oil may be used in the treatment of skin diseases and diarrhea etc. caused by microorganisms tested. Further toxicological and clinical studies are required to prove the safety of the oil as a medicine.
Acknowledgements
The author is thankful to Mr. Mohammad Mukhair, the technician of the center, for technical assistance. In addition, the author gratefully acknowledge the financial support of the Research Center at College of Pharmacy, King Saud University.