Total phenolic contents, antibacterial and antioxidant activities of some Thai medicinal plant extracts

Total phenolic contents, antibacterial and antioxidant activities of aqueous and ethanolic extracts from Thai medicinal plants were investigated in this study. The antibacterial activity was carried out using agar disc diffusion and broth dilution methods against Escherichia coli O157:H7, Propionibacterium acnes, Pseudomonas aeruginosa, Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pyogenes, and methicillin resistant S. aureus. The aqueous and ethanol extracts of Senna alata showed the most effective activity against Gram positive bacteria, with inhibition zone ranging from 10.3 to 23.0 mm. The highest activity was observed from S. alata extracts against P. acnes, with minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) values of 1.9 and 3.9 mg/ml, respectively. The antioxidant activity was evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2’– azinobis(3-ethylbenzothiazoline-6-sulfonic acid (ABTS) methods. The strongest antioxidant activities of aqueous extract of S. alata were 22.11 ± 0.324 mg gallic/g extract and 214.99 ± 17.279 mg trolox/g extract when determined by DPPH and ABTS assay, respectively. Moreover, the highest total phenolic content of 70.90 ± 1.048 mg gallic/g extract was measured from the aqueous extract of S. alata. Therefore, the biological activities of these plants observed in this study will be useful to develop the plant extracts for primary treatment of diseases as new therapeutic agents.   Key words: Medicinal plants, antibacterial activity, pathogenic bacteria, antioxidant activity, total phenolic content.