Composition and Antimicrobial Activity of Leaf Essential Oil of Teucrium mascatenses Boiss. from Oman, The

Journal of Essential Oil Research: JEOR, Jul/Aug 2006 by Hisham, Abdulkhader, Pathare, Nirmal, Al-Saidi, Salim, Al-Salmi, Ahmed

Abstract

A hydrodistilled oil from the leaves of Teucrium mascatense Boiss. was analyzed by GC/MS. Twenty-one components amounting to 91.2% of the oil were identified with linalool (27.8%), linalyl acetate (12.6%) and β-eudesmol (10.1%) being the major constituents of the oil. The antimicrobial activity of the oil was tested against a panel of 17 bacterial and six fungal strains by the disc diffusion method. The oil inhibited the growth of all test organisms at various levels. The minimal inhibitory concentrations (MIC) were also determined.

Key Word Index

Teucrium mascatensis , Lamiaceae, essential oil composition, linalool, linalyl acetate, β-eudesmol, antimicrobial activity.

Introduction

The genus Teucrium (Lamiaceae) is represented by about 300 species (1), of which 49 species are endemic to Europe mainly in the Mediterranean region and many of these species are used in the folk medicine of many countries as stimulants, tonics, stomach ache remedy and also as anti-diabetic agents (2). The Teucrium species are considered as potential source of neo-clerodane diterpenoids and they are rich in essential oils as well (2).

Even though, several reports deal with the essential oil composition of more than thirty Teucrium species, the studies on the species growingin this region is rather limited except for T. stocksianum (3,4), T. melissoides (5), T.flavum (6) and T. polium (7). In general, the essential oil chemistry of Teucrium dominates with sesquiterpe contents particularly compounds such as β-caryophyllene and germacrene D.

Teucrium mascatensis Boiss. is an aromatic perennial, a native plant of Oman, which grows 25 cm high and frequently seen on rocky hill and mountain slopes in northern Oman (8). It shares the common Arabic numeja'clah with a related species T. stocksianum Boiss., a plant more common throughout the Middle East and is popular for its use in folk medicine as a fever remedy. Teucrium mascatense is also used as a fever remedy as well to reduce the blood flow during menstruation. This Teucrium species is morphologically quite distinct from T. stocksianum and has neither been chemically nor pharmacologically investigated so far.

Experimental

Plant material used in this study was collected from the higher planes of 'green mountain' (Jabal Al-Akdhar in Arabic), the main mountain massif of northern Oman, situated 2800 in above the sea level, in April 2004 and authenticated by Annette Patzalt, Department of Botany, SQ university, Oman where a voucher specimen has been deposited.

Oil isolation: A sample of pleasant smelling genuine oil was isolated by hydrodistillation of 50 g shade-dried powdered aerial parts of T. mascatense using a Clevenger-type apparatus for four hrs (yield 0.8%).

Preliminary GC analysis: The preliminary GC analysis was carried out

by means of a HP 5890 gas chromatograph equipped with a HP-1-cross-linked methylsilicone gum capillary column (25 in x 0.32 mm x 0.52 µm film thickness), using a FID detector.

GC/MS analysis: The oil was diluted with an appropriate volume of dichloromethane and analyzed by GC/MS on a Shimadzu model (GC-MS-QP/5050A) instrument equipped with HP-5 (5%-phenyl)-methylpolysiloxane-nonpoIar-capiIlary column (30 m x 0.32 mm x 1.0 µm thickness) and interfaced with a quadrupole mass spectrometer.

Analytical conditions: The injector and interface temperatures were kept at 275°C and 300°C, respectively. The oven temperature was programmed from 70°-270°C at a rate of 3°C/min. Helium was used as the carrier gas with a linear velocity of 74.6 cm/s and the total flow rate was 39.9 mL/min. Mass spectra were continuously recorded from 40 to 500 m/z. The MS operating parameters were: ionization voltage 70 eV, scan rate 500 amu/s. The components of the essential oil were identified by comparison of their mass spectral data with the reference spectra (Wiley 229, 2000) in the data base.

Microbial cultures growth conditions: Test microorganisms included the following standard antimicrobial susceptibility strains: Staphylococcus aureus (NCTC 6571), Escherichia coli (NCTC10418), Pseudomonas aeruginosa (NCTC10662) besides a battery of Gram positive and Gram negative strains given in Table II as per the NCCLS guidelines (9). Cultures of these bacteria were grown in Mueller-Hinton broth (Difco) at 37°C and maintained on slopes of nutrient agar (Difco) at 4°C.

Antimicrobial activity assay: The oil was tested for antimicrobial activity using the disc diffusion technique on solid media as described by Bauer et al ( 10). Sterile, 6-mm diameter Whatman41 discs [containing filter sterilized oil initially diluted 4 mg/mL with ethylene glycol and further diluted to achieve required disc concentrations with phosphate buffered saline (w/v)] were placed on plates of Mueller-Hinton agar (Difco), which had been surface spread with 0.1 mL of logarithmic phase bacteria at a density adjusted to a 0.5 McFarland turbidity standard (108 colony-forming units [CFU]/mL). The plates were then incubated for 24 h at 37°C. Disc containing 0.04 mL ethylene glycol was placed in each plate as control. The results were recorded by measuring the average zones of growth inhibition surrounding the discs. Standard antibiotic discs as per the requirement of 'Laboratory Control and Antimicrobial Therapy'(11) were used in parallel. Antifungal disc diffusion assay was performed by employing above techniques utilizing Sabourauds agar and 0.2 mL culture suspension. The plates were incubated at 27°C for 48 h.