Chemical composition, antimicrobial potential against cariogenic bacteria and cytotoxic activity of Tunisian Nigella sativa essential oil and thymoquinone

We investigate in this work the chemical composition by GC-EIMS, the antibacterial and the cytotoxic activities of Tunisian Nigella sativa essential oil and its bioactive compound, thymoquinone, were tested against various clinical cariogenic bacteria (n = 30). Eighty-four compounds were identified in the essential oil. The major one was p-cymene (49.48%) whereas thymoquinone represented only 0.79%. The essential oil (2.43 mg/disc) containing only 3.35 mu g of thymoquinone showed pronounced dose dependant antibacterial activity against Streptococcus mitis, Streptococcus mutans, Streptococcus constellatus and Gemella haemolysans (15.5 +/- 0.707 mm). However, pure thymoquinone compound (150 mu g/disk) was active against all the studied strains especially S. mutans and S. mitis (24.5 +/- 0.71 and 22 +/- 1.41 mm inhibition zones, respectively). Their MIC values are representatives of a good effect. So, the essential oil strongest activity was seen against S. mitis, S. mutans, S. constellatus and G. haemolysans (MIC 2.13 mg/ml). However, thymoquinone was active against all the studied strains. The most important antibacterial activity was seen against S. constellatus (MIC 4 mu g/ml). The growth inhibition effects of thymoquinone on human epithelial cell lines (Hep-2) were significantly stronger than the essential oil. The IC50 of thymoquinone and essential oil were 19.25 +/- 1.6 and 55.2 +/- 2.1 mu g/ml, respectively. Our results demonstrate an important anticariogenic activity of the Tunisian N. sativa essential oil and thymoquinone. These effects further validate the traditional use of N. sativa in the folk medicine against various bacterial infections. (C) 2011 Elsevier Ltd. All rights reserved.