In vitro antibacterial, antioxidant activity and total phenolic content of some essential oils

In vitro antibacterial activity of 16 essential oils was investigated by disc diffusion method against two Gram positive bacteria Bacillus subtilis and Staphylococcus aureus and two Gram negative bacteria, Shigella flexneri and Escherichia coli. Oils of Cymbopogon citratus and Ocimum basilicum showed highest antibacterial activity. Gram positive bacteria were found to be more sensitive than Gram negative. Antioxidant activities were tested by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging assay and ABTS radical cation decolourization assay while Folin-Ciocalteu method was used to determine the total phenolic content. In DPPH assay, highest antioxidant activity was observed in O. basilicum oil followed by Azeratum conyzoides, A. marmelos and C. citratus, with percent inhibition and IC50 value ranging from 66.11-71.93% and 14.10-17.92 mu l ml(-1) respectively. In ABTS assay, similar results were obtained but with higher percent inhibition which ranged from 67.48-76.23% and lower IC50 value (12.12-17.21 mu l ml(-1)). Moreover, radical scavenging activity of essential oils was lower than that observed for the synthetic antioxidant BHA and BHT. The total phenolic content of the essential oils as GAE in mg 100 mu l(-1) of EO was found to be highest in O. basilicum (0.406) oil followed by A. conyzoides (0.322), A. marmelos (0.238) and C. citratus (0.231). The results provide evidence that the oils of C. citratus and O. basilicum can be further recommended for treatment of infections caused by these bacterial pathogens and are potential source of natural antioxidants having appreciable amount of total phenolic content.