Screening for Antibacterial and Antifungal Compounds in Bersama Abyssinica Fresen
Ong’era, Tabitha Nyanchoka
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Medicinal plants contain a wide range of substances that can be used to treat chronic illness as well as infectious diseases. A vast knowledge of how to use the plants against different illnesses may be expected to have accumulated in areas where plants are commonly used. Conventional medicine has created problems due to microbial resistance. This has enhanced the interest in search for natural products with medicinal property. Information on the chemical constituents in herbs aid in discovering new therapeutic drugs. Bersama abyssinica was selected for this study because of its uses in traditional medicine as an antimicrobial agent. For example, the bark, root, and leaf decoctions are taken to treat a range of stomach disorders such as abdominal pain, colic, diarrhoea, intestinal worms and amoebiasis. A stem bark decoction is drunk to cure cancer and rheumatism. The overall objective of this study was to extract, isolate and characterize bioactive compounds with antibacterial and antifungal activities in Bersama abyssinica. Crude extracts of the stem bark was bioassayed for antibacterial and antifungal activities. Column chromatography, thin layer chromatography and vacuum liquid chromatography were used for separation, isolation and purification of the extracts. Spectroscopic techniques were used to elucidate their structures. Six compounds were isolated which include: β-sitosterol (TN4), β-stigmasterol (TN3), β-sitosterol glycoside (TN2), lupeol (TN5), oleanolic acid (TN6) and an anthraquinone [Bersamanone] (TN1). From the isolated compounds, five have been previously reported in literature while Bersamanone is reported for the first time from this plant species. The bacteria used to test for antibacterial activities included Salmonella typhi, Shigella dysentriae, Vibrio cholerae, Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis while the antifungal test was carried out against Candida albicans and Penicillium notatum. Dichloromethane extract of the stem bark had mild activity of 8 and 9 mm on Bacillus subtilis and Staphyloccocus aureus, respectively. Ethyl acetate extract had moderate activity of 10 and 10 mm on Staphyloccocus aureus and Bacillus subtilis. It had mild activity on the other strains of bacteria. Antifungal activities of this extracts were also mild on Candida albicans and Penicillium notatum. Methanol extract had the highest activity of 16 and 16 mm on Klebsiella pneumoniae and Pseudomonas aeruginosa, respectively. Moderate activity was shown in Vibrio cholerae, Escherichia coli, Bacillus subtilis and Staphylococcus aureus. Among the compounds isolated β-sitosterol glucoside had activity against all the strains of bacteria and fungi the highest being that of B. subtilis and E. coli with inhibition zones of 14 and 15 mm, respectively. The anthraquinone had activity against Bacillus subtilis, Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli with inhibition zones of 14, 9, 14 and 10 mm, respectively. Lupeol had moderate activity against Bacillus subtilis, Staphylococcus aureus and Escherichia coli with inhibition zones of 11, 14 and 8 mm, respectively. The study showed that the studied plant species contain compounds that showed varied bioactivities on the test bacteria and fungi and can be used in treatment of the diseases caused by respective pathogens used in this study once cytotoxicity tests are done.