Chemical composition and antibacterial activity of essential oil of Nepeta graciliflora Benth. (Lamiaceae)

Abstract The chemical composition of the essential oil obtained from aerial parts of Nepeta graciliflora was analysed, for the first time, by GC–FID and GC–MS. A total of 27 compounds were identified, constituting over 91.44% of oil composition. The oil was strongly characterised by sesquiterpenes (86.72%), with β-sesquiphellandrene (28.75%), caryophyllene oxide (12.15%), α-bisabolol (8.97%), α-bergamotene (8.51%), β-bisabolene (6.33%) and β-Caryophyllene (5.34%) as the main constituents. The in vitro activity of the essential oil was determined against four micro-organisms in comparison with chloramphenicol by the agar well diffusion and broth dilution method. The oil exhibited good activity against all tested organisms.


Introduction
The genus Nepeta, which belongs to the family Lamiaceae, is an annual herb comprised of about 300 species which are spread out over a large part of Europe, Asia and Africa (Rechinger 1982;Formisano et al. 2011). In India about 30 species are found, widely distributed in temperate Himalayas, and on foothills and plains (Hooker 1975;Rechinger 1982). The genus Nepeta shows diverse biological behaviour like feline attractant, canine attractant, insect repellant and arthropod defence (Wagner & Wolf 1977;Bottini et al. 1987;Gkinis et al. 2003).
Nepeta graciliflora (common name: Uprya ghas) is reported as an ethno-medico-botanical herb of Uttarakhand (Bisht, Rana, et al. 2012). Based on the existing literature on N. graciliflora and ethnobotanical principles of essential oils from the species of Nepeta genus, aerial parts of N. graciliflora have been investigated for the first time. As such the objective behind present work was to evaluate the chemical composition and antibacterial activity of essential oil from aerial parts of N. graciliflora.

Antibacterial activities
The antibacterial activity of essential oil was tested against four bacteria, by evaluating the presence of inhibition zone diameter and minimum inhibitory concentration (MIC), as presented in Table S2. The oil inhibited the growth of all tested micro-organisms with zone inhibition diameter from 16 to 33 mm and MIC ranging from 114 to 260 μg mL −1 (Table S2). Among all tested micro-organisms, oil showed good activity against Bacillus cereus with MIC 114 μg mL −1 followed by Staphylococcus aureus, Pseudomonas aeruginosa and Klebsiella pneumoniae having MIC values of 123, 212 and 260 μg mL −1 , respectively. These results suggested that the extracted oil of N. graciliflora has capacity to inhibit the growth of selected bacterial strains.

Disclosure statement
No potential conflict of interest was reported by the authors.

Supplementary Data and research material
The experimental details relating to this article are available online http://dx.doi.org/10.10 80/14786419.2015.1055489.