The variation in antimicrobial and antioxidant activities of acetone leaf extracts of 12 Moringa oleifera (Moringaceae) trees enables the selection of trees with additional uses

Abstract

BACKGROUND : The aim of this study was to evaluate the variation in antimicrobial and antioxidant activities of the leaf acetone extracts of 12 Moringa oleifera trees harvested in order to select the best material for clonal propagation. METHODS : A two-fold serial microdilution method was used to determine the minimum inhibitory concentration (MIC) against a panel of fungal (Candida albicans, Aspergillus fumigatus and Cryptococcus neoformans) and bacterial (Staphylococcus aureus, Enterococcus faecalis, Escherichia coli and Pseudomonas aeruginosa) species. The radical scavenging capacity was determined using 2,2 diphenyl-1-picryhydrazyl (DPPH). RESULTS : There was a large variation in antimicrobial activities with MICs between 0.04 and 2.50 mg/ml against bacteria and from 0.16 to N2.50 mg/ml against fungi. For samples harvested in winter: trees L3 and LP2 had significant activity against E. faecalis (MIC 0.08 mg/ml) and E. coli (MIC 0.04 mg/ml). Trees L5, LP1 and LP6 had weak activity against E. coli (MICs 1.25 and 2.50 mg/ml), S. aureus (MIC 1.25 mg/ml), and E. faecalis (MIC 2.50 mg/ml), while other samples had moderate activity against the four bacteria (MICs 0.16–0.63 mg/ml). From samples collected in summer: L5 (MIC 0.08 mg/ml), L6 (MIC 0.08 mg/ml after 1 h incubation), LP1 (MICs 0.08 mg/ml), LP2 (MICs 0.08 mg/ml after 1 h incubation), LP4 (0.08 mg/ml) and LP5 (MICs 0.04 and 0.08 mg/ml) had significant activity against E. faecalis (L5, L6, LP1, LP2, LP4, and LP5), S. aureus (LP1, and LP5), and E. coli (LP2, and LP5), respectively. Other extracts had weak antibacterial activity with MICs ranging from 0.16 to 0.63 mg/ml. Most of the samples harvested in winter had moderate antifungal activity: L1, L2, L3, L4, L5, L6, LP1, LP2, and LP3 had moderate activity against C. albicans (ATCC strains) with MIC of 0.63 mg/ml in all cases while L2, L3 and L4 as well as L6, LP1, LP2, LP3, LP5 and LP6 against A. fumigatus (MICs 0.63 mg/ml) and C. neoformans (MICs 0.63 mg/ml), respectively. Apart from L1 (MIC 0.31 mg/ml), L2, L3 and LP6 (MICs 0.63 mg/ml in all cases) with moderate activity, all the samples collected during summer had weak activity against A. fumigatus (MICs 1.25–2.50 mg/ml). All the extracts had a low radical scavenging activity with the IC50 values ranging from 34.72 to 109.62 μg/ml, compared to the reference standard L-ascorbic acid (IC50 2.41 μg/ml). This may be related to the extractant used. CONCLUSION : The large variation in antimicrobial activity and antioxidant activities of 24 acetone leaf extracts of 12 M. oleifera trees may lead to the selection of clonal material to serve as a source of propagation materials. Successful propagation and growth of tree LP with very good activity against E. coli and a high total activity could provide an additional use of this valuable plant species to rural people.