ANTIBACTERIAL AND ANTIOXIDANT ACTIVITIES OF TWO PLANTS FROM NILGIRIS OF INDIA

Abstract

Our objective is to evaluate the antibacterial and antioxidant activity of ethanolic extracts of Plectranthus mollis (P.mollis) and Salvia officinalis (S. officinalis) leaves locally used for treatment of microbial infection in Nilgiris of India. Antibacterial activity was determined by using agar diffusion and broth dilution methods against seven microorganisms. The antioxidant potential was assessed by using 2,2 diphenyl -1- picryl hydrazine (DPPH) scavenging assay. Ethanolic extract of P. mollis showed antibacterial activity  in the following order viz Pseudomonas aerugenosa (20 mm, MIC of 12.5 µg/ml), Staphylococcus aureus (19 mm, MIC of 6.3µg/ml), Bacillus cereus (18 mm, MIC of 25µg/ml), Salmonella typhimurium (16 mm, MIC of 25µg/ml) and Bacillus subtilis (14 mm, MIC of 12.5µg/ml). Escherichia coli and Klebsiella pneumoniae were resistant to ethanolic extract of P.mollis, whereas the ethanolic extract of S. officinalis and control (DMSO) did not show any inhibition against all the bacteria tested. Both the extracts possess marked DPPH radical scavenging activities compared to the reference antioxidant ascorbic acid in a dose dependent manner with the IC₅₀ values being 73.26µg/ml, 107µg/ml and 40.17µg/ml for P. mollis, S. officinalis and ascorbic acid respectively. Based on the results, it may be confirmed that the antioxidants might have enhanced the antibacterial activities of P.mollis. But S. officinalis did not show any antibacterial activities even though it has good antioxidant potential than P.mollis. Further studies on isolation and purification of compounds that are responsible for their antibacterial and antioxidant activities are needed.