A study of Nigella sativa seed for antimicrobial activity with special reference to resistant bacteria

Nigella sativa seed, used for centuries for medicinal and culinary purposes and reported to possess a number of pharmacological properties, including antimicrobial, was studied for antibacterial activity against standard strains and clinical isolates. Its various extracts and oil (Commercial) were tested in varying concentrations by Disc Agar diffusion technique using impregnated filter paper discs on inoculated Muellar Hinton agar plates. Commercial antibiotic sensitivity testing discs were used for sensitivity testing and comparison.

After Soxhlet extraction, yield was 32.5%, 27% and 16.7% with methanol, water and ether respectively. Extraction by soaking method gave 28- 31% yield of the above. Methanolic extract and oil showed pronounced dose dependant activity even upto 1:200 dilution whereas aqueous and ether extracts showed variable results. Antibacterial activity was more against gram +ve than gram –ve bacteria. Among gram +ve bacteria tested, Bacillus subtilis, Staph. aureus,  Staph. Epidermidis, other coagulase –ve Staphylococci and Strept. pyogenes were sensitive to extract and oil and 2 (Enterococcus faecalis, Strept. agalactae) were resistant. Among gram –ve bacteria tested, E. coli and Psdm. aerugenosa were sensitive to extract, only P. aerugenosa to oil and rest (Acinetobacter baumannii, Citrobacter fecundii, Klebsiella pneumoniae, Proteus mirabilis, P. vulgaris, S. typhi, Shigella bodyii and Vibrio cholerae) were insensitive. Out of 158 strains tested, most of them were resistant to a number of antibiotics, 102 were inhibited by methanolic extract and 97 by oil.

Our results are in conformity with earlier reports. However, to the best of our knowledge, the activity of methanolic extract as well as of essential oil against S. aureus (ATCC 25923, NCTC 6571 strains), P. aerugenosa (ATCC 27853, NCTC 10662 strains), coagulase negative Staphylococci (except S. epidermidis) and Strept. Pyogenes; and of methanolic extract against E. coli (ATCC 25922, NCTC 10418 strains) is being reported for the first time by us.

The drug (N. sativa oil/ methanolic extract) is found active against standard as well as multi drug resistant strains of tested bacteria. The antibacterial activity appears to be due to Thymol, Thymoquinone, Thymohydroquinone and tannins.