Antioxidant and the antimicrobial activities of aqueous and ethanolic extracts of purple coneflower (Echinacea purpurea L.) against some gram positive and gram negative bacteria

In recent years study of medicinal plants in order to discover new pharmaceutical supplies against microbial strains has been considered very much. The main objective of this study was to evaluate the antioxidant and antimicrobial activities of shoot aqueous and ethanolic extracts of purple coneflower against some gram positive and gram negative bacteria.

This experimental study was conducted in 2018 at Bu- Ali Sina University. Maceration method and solvent of water and ethanol at a ratio of 1 to 5 used for extraction. The total phenolic contents of the extracts were measured by Folin-ciocalteau method. Then, the amount of cichoric acid of purple coneflower was determined using by high performance liquid chromatography. Antioxidant activity of different concentration of extracts were assessed by diphenyl picrylhydrazyl radical-scavenging activity and compared with synthetic antioxidant butylated hydroxyl toluene (BHT). The micro-organisms investigated in this study were:  Staphylococcus aureus, Staphylococcus epidermidis, Listeria innocua, Bacillus cereus, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhimurium and Shigella flexneri. The antimicrobial activity of aqueous and ethanolic extracts was tested by pour plate, agar well diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) methods. Also interaction of these extracts was also studied by FICindex determination using modified dilution checkboard method. Experimental data were analyzed using ANOVA by the SPSS version 20 software and mean comparison were done using the t-test and Duncan's multiple range test.

The results showed that the ethanolic extract had the highest total phenolic content and cichoric acid. The ability of purple coneflower aqueous and ethanolic extracts in scavenging free radicals was found to be higher in the ethanolic extract with a concentration of 3000 μg/ml. The aqueous extract of purple coneflower at the concentrations of 25 and 50 mg/ml has no inhibitory effect on gram negative bacteria growth. The maximum diameter of inhibition zone of aqueous or ethanolic extracts of this plant in a concentration of 400 mg/ml pertained to the bacterium Staphylococcus aureus. The minimum zone diameter in this concentration was associated with Pseudomonas aeruginosa. Furthermore, purple coneflower extracts showed greater inhibitory effect on gram positive bacteria in comparison with gram negative bacteria. Also the results showed that ethanolic extract had greater inhibitory effects on the strains studied compared to aqueous extract. The MIC of purple coneflower ethanolic extract ranged from 16 to 256 mg/ml, depending on the type of bacteria (gram positive or gram negative).

These findings showed that ethanolic extract of purple coneflower has antimicrobial effects on gram positive bacteria and can substitute for chemical preservatives.
Key words: Purple coneflower extract, Phenolic compounds, Cichoric acid, Antimicrobial activity, Radical scavenging