Correlation between in vitro antioxidant and antibacterial activities against some pathogenic bacteria of some essential oils

Cold press essential oil samples from four different spice types ( Urtica dioica (seed), Punica granatum(seed) Cannabis sativa L., Coriandrum sativum, Carthamus tinctorius , Vitis vinifera ) and Pistacia terebinthus ) and their basic ingredients were tested for their inhibitory effect against 14  strains of bacteria (gram-positive, gram-negative) and 2 yeast strains. Preliminary screening of antimicrobial activity of the essential oils was done using the filter paper disc agar diffusion method. The essential oils were diluted at different ratios as 1/20 and 1/30 with analytical grade alcohol and hexane. Some of the essential oils were sufficient to prevent microbial growth at fairly high concentrations (10 – 30 mg/ml). The most sensitive organisms were fungus in among the tested microorganisms. The data showed that Gram- negative bacteria were more sensitive to the antimicrobial compounds in spices than positive. The most sensitive microorganisms were  Candida albicans, Aspergillus niger and  Micrococcus luteus. The inhibition zones of different microbial growth produced by various essential oils were not similar to those produced by their basic compounds. There was a relationship between the chemical structures of the most abundant compounds in the essential oils under investigation and the antimicrobial activity. The antioxidant activities of these samples were also evaluated based on different methods (DPPH and ABTS radical scavenging activities and FRAP assay). According to these three methods, the essential oil of the pomegranate ( P. granatum ) seed had the highest antioxidant activities. Unlike, essential oil sample obtained from stinging nettle ( U. dioica) seeds exhibited the lowest values. The results showed that the essential oil of coriander ( C. sativum ) had the highest antioxidant activity values. Grape vine ( V. vinifera ) had the lowest antioxidant activities based on DPPH and ABTS assays while cannabis ( C. sativa L . ) had the lowest activity in terms of FRAP values.