Antibacterial activity of Nigella sativa seed essential oil and effect of different extraction methods on content of its active principle, thymoquinone

Nigella sativa L. is used in folk medicine all over the world for the treatment of a number of diseases. Its seed essential oil (EO) has previously demonstrated a wide range of biological activities, including antimicrobial effect [1]. In our study, we aimed to determine the influence of four different extraction methods on the chemical composition and antimicrobial activity of N. sativa seed EO, as well as on the content of its active principle, thymoquinone. EOs extracted by hydrodistillation (HD), dry steam distillation (SD), steam distillation of crude oils obtained by solvent extraction (SE/SD), and supercritical fluid extraction (SFE/SD) were tested for their antibacterial activities using broth microdilution method [2] against Bacillus cereus , B. subtilis , Bacteroides fragilis , Enterococcus faecalis , Escherichia coli , Pseudomonas aeruginosa , Staphylococcus aureus , S. epidermidis , and Streptococcus pyogenes. All samples were subsequently analyzed by gas chromatography and gas chromatography-mass spectrometry. The results showed that the EOs obtained by HD and SD were dominated by p -cymene, whereas the major constituent identified in both volatile fractions obtained by SD of extracted oils was thymoquinone (ranging between 0.36 and 0.38mg/mL, whereas in oils obtained by HD and SD it constituted only 0.03 and 0.05mg/mL). Both oils distilled directly from seeds showed lower antimicrobial activity (MICs ≥512 and 256 µ g/mL for HD and SD, respectively) than those obtained by SE/SD and SFE/SD (MICs ≥4 µ g/mL). Thymoquinone exhibited potent growth-inhibiting activity against Gram-positive bacteria with MICs ranging from 8 to 512 µ g/mL. Acknowledgements: This research was supported by projects GACR 104/06/1174 and GA AV Z4 055 0506. References : 1. Ali, B.H., Blunden G. (2003), Phytother. Res. 17: 299–305. 2. Jorgensen, J.H. et al. (1999), Manual of Clinical Microbiology, Murray, P.R. ed., ASM Press, Washington, DC.