Isolation and identification of antimicrobials from erythrina excelsa bak
Ombuna, Naftal M.
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Microbial infections constitute a serious problem especially in developing countries. Several antibiotics have been developed but their use is limited due to antimicrobial resistance and emergence of new infections. Several plants have proven to be medicinal and this has necessitated research in the field of phytochemistry aimed at generating more effective antimicrobial agents. The aim of this study was to investigate the phytochemical properties with respect to antimicrobial effects of the crude and pure components from extracts of Erythrina excelsa against chosen available micro-organisms. The stem bark of E. excelsa was air dried under a shade and ground into fine powder. It was soaked sequentially using the solvents; n-Hexane, dichloromethane, ethyl acetate and methanol for 48 hours, decanted and the extracts concentrated under reduced pressure in a rotary evaporator. The crude extracts obtained were tested against two Gram-positive bacteria species; Staphylococcus aureus (ATCC 35844) and Bacillus subtillis (ATCC 6051), one Gram-negative bacteria; Escherichia coli (ATCC 11775) two fungal strains; Aspergilus niger and Candida albicans. Gentamycin and Nystatin were used as standard antibiotics. Gentamycin had an inhibition zone of 17.00±0.00 mm against the micro-organisms tested. Methanol extract was highly active with inhibition zones of 15.10±0.10 mm against S. aureus and 14.10±0.10 mm against both B. subtillis and E. coli. Ethyl acetate had a moderate activity 13.10±0.10 mm against S. aureus while dichloromethane had mild activity with its lowest inhibition zone being 7.10±0.00 mm against E. coli. In antifungal tests, Methanol extract had highest activity of 15.10±0.10 mm against A. niger and 13.10±0.10 mm against C. albicans. Dichloromethane extract was moderately active with inhibition zones of 14.10±0.10 mm against A. niger and 12.10±0.00 mm against C. albicans while ethyl acetate had mild activity of 10.10±0.17 mm against A. niger. Positive control Nystatin had an inhibition zone of 16.00±0.00 mm. GC-MS was used to detect the class of compounds present in E. excelsa such as terpenoids, phenols, fatty acids and their derivatives. The isolation and purification of compounds was done using column chromatography and preparative thin layer chromatography yielding a total of five compounds; Glutinosalactone A (55) and glutinosalactone B (56) which exhibited mild activity against the tested organisms. Glutinosalactone A (55) had inhibition zone of 10.10±0.10 mm against E. coli, and 11.10±0.10 mm against both S. aureus and B. subtillis while glutinosalactone B (56) had inhibition zones of 11.10±0.10 mm against B. subtillis and 10.10±0.10 mm against both S. aureus and E. coli. These compounds were also active against A. niger and C. albicans with glutinosalactone A (55) having highest inhibition zones of 15.10±0.03 mm against A. niger and 11.00±0.00 mm against C. albicans. Lupinifolin (57), sitosterol (58) and 3β-stigimasterol (59) had mild activity of 9.00±0.03, 8.00±0.03 and 8.10±0.03 mm against A. niger respectively. The structures of isolated compounds were elucidated using physical properties such as melting point and Spectroscopic techniques such as IR, 1D and 2D-NMR. The results obtained from the crude extracts and the isolated compounds show that E. excelsa contain bioactive compounds. The isolated bioactive compounds can also serve as templates for synthesis of more potent drugs.