Composition and antimicrobial activity of Juniperus excelsa essential oil

Abstract

The genus Juniperus (Cupressaceae) consists of 55 species, all of which occur throughout the northern hemisphere of the world [1]; eigth species of them grow in Turkey [2]. Evergreen shrubs and trees in this conifer genus are slow growing and long lived. Various species of juniper are used medicinally with a range of applications from antiseptic to diuretic [3, 4]. Juniperus excelsa M. Bieb. is a medium-sized shrub or tree up to 20 m. This species was divided into 2 subspecies (subsp. excelsa and subsp. polycarpos) by Farjon: one with a distribution in southeastern Europe, the Crimea, and mainly southern Turkey to Lebanon; the other a more continental element extending from North Turkey to Kirgizistan and Pakistan [5]. Subspecies excelsa is the subject of this paper. This subspecies is widespread in Turkey but most common in South Anatolia, in dry rocky slopes in hills and mountains at between 150‐2700 m, often forming the tree line in the Taurus mountains [5]. It is locally known as “boylu ardic” tall juniper in Turkey [6]. The chemical composition of the leaf and wood essential oils from Juniperus excelsa were previously reported [7‐9]. In the literature, there are a number of reports on the composition of the essential oil from berries of Juniperus species and their antimicrobial activities [10‐13]. Hexane and methanol extracts of J. excelsa were reported to demonstrate antimicrobial activity against microorganisms, including Mycobacterium tuberculosis [14]. The antimicrobial activity of J. excelsa essential oil against three standard bacterial strains and the yeast Saccharomyces cerevisiae have been reported [15]. The objective of this study was to determine the in vitro antimicrobial activity of the essential oil of the berries of J. excelsa and its main component, α-pinene, against clinically important microorganisms, including an anaerobic bacterium and the pathogenic yeasts. GS/MS analysis of J. excelsa essential oil resulted in the identification of forty-four constituents [16], representing 91.3% of the oil, as shown in Table 1. The major components were α-pinene (55.5%), α-cedrol (7.7%), sabinene (3.5%), and verbenone (2.4%). Similarly, Topcu et al. reported α-pinene (34.0%) and α-cedrol (12.3%) as the major components in the essential oil from berries of J. excelsa [17]. In another study, the main constituents were found to be α-pinene (29.1%) and carene (29.1%) [15]. The differences in the content of the oils might result from geographical origin, edaphic factors, or harvesting time. Antimicrobial chemotherapy has not achieved the much required success in the eradication of microbial infections because of the antimicrobial resistance developed by most pathogenic microorganisms. The antimicrobial properties of essential oils derived from many plants are under extensive study. The assays were performed as described elsewhere [18]. The results of this study shows that J. excelsa essential oil has a strong activity against the anaerobic bacterium Clostridium perfingens while exhibiting moderate activity against Staphylococus aureus, Streptococcus pyogenes, Streptococcus pneumoniae, Mycobacterium smegmatis , Candida albicans, and Candida krusei (Table 2). The data presented here are consistent with the previous studies which demostrated that α-pinene is a slightly active component [18]. The MICs of the main component of the essential oil, α-pinene, were also determined in parallel experiments, proving that this constituent is responsible for the antimicrobial activity, at least against C. perfringens and yeasts. Each plant extract and essential oil con tain complex mixtures of volatile and non-volatile compounds, and little is known about the effect of interactions between individual constituents on antimicrobial activity. Interactions between these components and known antibiotics may also lead to additive, synergistic, or antagonistic effects.