Antimicrobial activities of Iranian sumac and avishan-e shirazi (Zataria multiflora) against some food-borne bacteria

Food poisoning originating from contaminated foods by both Gram-positive and Gram-negative bacteria causes concern to society and to the industry. Spices have been used safely since ancient times as food flavoring agents and also as herbal medicines and are now mainly considered “generally regarded as safe” (GRAS). Antimicrobial effects of two spices used in Iranian traditional medicine were investigated against some pathogenic food-borne bacteria. Hydroalcoholic extracts of Rhus coriaria L. (sumac) and Zataria multiflora Boiss. (avishan-e shirazi or zaatar) obtained from Tehran botanicals market were prepared by cool percolation method using 80% (v/v) aqueous alcohol. Antimicrobial activities of the extracts were tested against several Gram-positive and Gram-negative bacteria including Staphylococcus aureus, Bacillus cereus, Escherichia coli, Salmonella typhi, Proteus vulgaris, and Shigella flexneri. All the extracts were primarily screened for their possible antimicrobial effects using disc and well diffusion methods. Both R. coriaria L. and Z. multiflora Boiss. showed considerable antibacterial effects. The potential antibacterial activities of the two herbal extracts were further investigated at concentrations of 0.05%, 0.1%, 0.2%, 0.4%, 0.8% and 1.6% (w/v) and minimum inhibitory concentration (MICs) as well as minimum bactericidal concentrations (MBCs) of the extracts were elucidated. Sumac showed better activity against the tested bacteria compared to avishan-e shirazi inhibiting Bacillus cereus and Staphylococcus aureus at concentrations of 0.05% and 0.1%, respectively while Gram-negative bacteria were affected by higher concentrations of sumac ranging 0.1–2%. The MICs of avishan-e shirazi against the tested bacteria ranged from 0.4% to 0.8%. Salmonella typhi was found to be the most resistant showing the MICs of 0.2% and 0.8% with sumac and avishan-e shirazi, respectively. Both popular Iranian spices which are traditionally used as astringent agents have promising inhibitory effects on food-borne bacteria and could be considered as natural food preservatives.