The growth-inhibitory effect of thymohydroquinone and thymoquinone on oral pathogenic bacteria in vitro

Nigella sativa L. is annual herb used in folk medicine all over the world for the treatment of a number of health disorders [1]. Its seed extracts have previously been observed to possessed broad spectrum of antimicrobial activity [2], including inhibitory effect on microorganisms isolated from oral cavity [3]. Although thymohydroquinone (THQ) and thymoquinone (TQ) have previously been identified as main antimicrobially effective quinone constituents of N. sativa seeds [4,5] their growth inhibitory effect against oral microorganisms has not been previously described.

Thus we decided to evaluated THQ and TQ for their potential antibacterial activity against oral bacteria involved in the pathogenesis of dental caries and periodontal diseases using the broth microdilution method [6]. TQ was purchased from Sigma-Aldrich (Prague, CZ) and THQ was prepared by reduction of thymoquinone, as described by El-Dakhakhny [7].

The results showed that both quinone compounds tested in this study possessed significant effect against oral pathogenic microorganisms, whereas Streptococcus mutans and S. sobrinus were found to be the most sensitive species with minimum inhibitory concentrations ranging from 8 to 16µg/ml.

Acknowledgements: Czech Science Foundation (project no. 525/08/1179).

References: [1] Ali, B.H., Blunden, G. (2003) Phytother. Res. 17:299–305.

[2] Hanafy, M.S.M., Hatem, M.E. (1991)J. Ethnopharmacol. 34:275–278.

[3] Chaudhry, N.M.A. et al. (2008) Pak. J. Bot., 40:461–467.

[4] El-Alfy, T.S. et al. (1975) Pharmazie 30:109–111.

[5] Kokoska, L. et al. (2008)J. Food Prot. 71:2475–2480.

[6] Jorgensen, J.H. et al. (1999). In: Murray P.R. (ed.) Manual of Clinical Microbiology. ASM Press. Washington, DC.

[7] El-Dakhakhny, M. (1963) Planta Med. 11:465–470.