Antimicrobial activity of individual and combined extracts of selected spices against some pathogenic and food spoilage microorganisms

Spices are indispensable components of Indian cuisines since ancient times and are considered as rich source of bio-active antimicrobial compounds. Antibacterial and antifungal activity of individual as well as ethanolic extracts of cumin (Cuminum cyminum), ginger (Zingiber officinale) and garlic (Allium sativum) was evaluated against bacterial strains of Bacillus subtilus, Pseudomonas fluroscens, Salmonella Typhi and fungal strains of Candida albicans and Rhizopus azygosporus. Agar well diffusion assay for antimicrobial activity yielded the inhibitory zone of 12.8 to18.3 mm diameter for cumin, 11.5 to 16.3 mm diameter for ginger and 16.8 to 19.3 mm diameter for garlic extract indicating that garlic was the most effective spice in inhibiting the microbial growth. The combined extracts showed inhibition zones ranging from 12.3 to 19.6 mm in diameter against bacteria and 15.6 to 19.6 mm against fungus. The combined extract of cumin and garlic was found to be most effective in inhibiting the microbial growth. The MIC of individual extracts was 12.5 mg/ml against all the tested microorganisms. The MIC of combined extracts fluctuated from 3.8 to 6.7 mg/ml and the most sensitive microbial species in relation to the MIC of combined extracts was S. Typhi. The fractional inhibitory concentrations (FIC) values of the combined extracts suggested additive inhibitory effect of the combined spice extracts (0.5 ≤ FIC index ≤ 1).