ANTIOXIDANT AND ANTIMICROBIAL STUDIES OF MEDICINAL PLANT EXTRACTS OF AFRICAN BIRCH (Anogeissus leiocarpus), ZOGALE (Moringa oleifera) AND AFRICAN CUSTARD APPLE (Anona sengalensis)

Ethanol extracts of three selected Nigerian medicinal plants-Anogeissus leiocarpus (African birch), Moringa oleifera (Zogale) and Anona senegalensis (African custard –apple) were assessed for antioxidant and antimicrobial properties. Phytochemical screening gave positive tests for the following bioactive compounds: tannins, flavonoids, cardiac glycosides, alkaloids, Saponin, anthraquinones and steroids. The antimicrobial sensitivity test of the plant extracts was determined in vitro using the agar well diffusion method against clinical isolates of Bacillus subtilis, Escherichia coli, Candida albicans, Trichophyton rubrum and Trichophyton mentagrophytes at concentrations from 400mg/ml to 50mg/ml, Gentamycin and Fluconazole were used as standards. The minimum inhibitory concentration (MIC) and minimum bacteriocidal concentration (MBC) of the extracts were determined. The antioxidant property was determined using 3-(4,5-dimethylthiazole-2-yl)-2,5-diphenyl tetrazolium bromide (MTT ) antioxidant assay method . Absorbance readings were taken at the wavelengths of 492nm and 620nm. Ascorbic acid was used as positive control and Dimethyl sulfoxide (DMSO) as the negative control. The MIC for A. senegalensis against both B. subtilis and E. coli was 12mg/ml while A. leocarpus has an MIC of 50mg/ml for both microorganisms. The MIC for M. oleifera was 6.2 mg/ml against B. subtilis and 12.5 mg/ml against E. coli. The MBC for A. leoicarpus was 100mg/ml for both B. subtilis and E. coli. A. senegalensis exhibited an MBC of 25mg/ml for both B. subtilis and E. coli while Moringa Oleifera had an MBC 25mg/ml against E. coli and 12.5 mg/ml against B. subtilis showing a higher activity. At the lowest concentration of 0.625mg/ml, A. leiocarpus had absorbance of 0.37 and 0.41 at 492nm and 620nm wavelength respectively. A. senegalensis had absorbance of 0.18 and 0.17 while absorbance of 0.12 and 0.11 were recorded for M. oleifera at 492nm and 620nm wavelengths respectively. The absorbance of Ascorbic acid at 0.625 mg/ml was 0.5 at 492nm wavelength and 0.36 at 620nm wavelength. The result indicated that the activity of all the extracts were best at 620nm wavelength. The antioxidant activities M. oleifera- and A. senegalensis are comparable to that of ascorbic acid but ascorbic acid has a better antioxidant activity with an absorbance of 0.36 at the lowest