Antibacterial, antifungal and phytochemical screening of the plant species lannea schweinfurthii (engl.) engl.
Kihagi, Regina Wamuyu
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Herbal medicine has been widely used and forms an integral part of primary health care in most countries. Of late, despite emphasis being put in research of synthetic drugs; interest in medicinal plants has been reborn. This is due to the rapidly growing population, the failure of modern medicine to provide effective treatment, increase in chronic diseases and the emergence of the multi-drug resistant pathogens. It is of importance to establish a scientific basis for the use and validation of medicinal plants through biological screening. Phytochemicals are currently receiving more attention due to their effectiveness in the treatment of infectious diseases as well as mitigating many of the side effects caused by conventional antimicrobials. Pharmacological studies of Lannea schweinfurthii (Engl.) Engl. has revealed antimicrobial property of the plant but very little has been reported about the active ingredients in the plant. In this study the stem bark of L. schweinfurthii (Engl.) Engl. was collected, air-dried and ground into a fine powder. Sequential extraction was done with hexane, dichloromethane (DCM), ethyl acetate (EtOAc) and methanol (MeOH). The crude extracts were subjected to bioassay screening for their antibacterial activity against selected strains of bacteria, including Gram-positive Staphylococcus aureus and Bacillus subtillis and Gram-negative Pseudomona aeruginosa and Escherichia coli and antifungal activities against Candida albicans. Moderate and high activities, ranging from 11 to 21 mm inhibition zones, were observed for EtOAc and MeOH crude extracts against the microbes used except P. aeruginosa. Hexane and DCM crude extracts showed mild activity of 7 mm. Tetracycline and nystatin used as positive controls for bacteria and fungi, respectively had inhibition zones of 18 mm. GC-MS analysis was done on the crude DCM and MeOH extracts to give a preliminary idea of the class of compounds in the plant species. The spectral data obtained from the crude DCM and MeOH extracts indicated presence of phenolic compounds, fatty acids and their derivatives, terpenoids, polyketide derivatives and steroids in the plant. Purification of crude extracts was carried out using solvent partition and chromatography: CC, VLC and PTLC. Structural elucidation and characterization was done using standard spectroscopic methods (1H NMR, 13C NMR, DEPT and COSY). The combined hexane/DCM extract yielded two compounds namely; 3-(10’-tridecenyl) phenol (LS01) and di-(2’-ethylhexyl) ester phthalic acid (LS05). Ethyl acetate extract gave three compounds namely; lupeol (LS02), β-sitosterol (LS03) and epicatechin (LS04). Bioassay of the isolated compounds was done in which epicatechin (LS04) showed high activity against the Gram-positive bacteria S. aureus and B. subtillis and Gram-negative E. coli, with an inhibition zone of 15, 14 and 10 mm, respectively. Further, epicatechin (LS04) showed an activity of 14 mm against C. albicans. The study has demonstrated that the stem bark of L .schweinfurthii has chemical constituents that are bioactive. Further studies such as cytotoxicity tests should be carried out on the crude extracts and isolated compounds to ascertain reported activity so to use bioactive components either as antimicrobials or as templates in drug synthesis. Furthermore, measures should be put in place to conserve the plant species from extinction.