ABSTRACT
Medicinal plants are a rich source of phytochemicals, and are used traditionally for treatment of many ailments, and thus are of great ethnomedicinal importance. This study presents work on phytochemical analysis, in vitro antimicrobial activity and cytotoxicity evaluation of medicinal plant Hydnora abyssinica. H. abyssinica is a medicinal plant indigenous to Namibia, Kenya, Democratic Republic of Congo (DRC), South Africa and Sudan. Preliminary phytochemical screening was done by colorimetric tests, while total phenol content (TPC), total flavonoid content (TFC) and total tannin content (TTC) were determined using spectrophotometric methods. Antimicrobial activity of the extracts was determined by means of agar diffusion and broth microdilution methods. Cytotoxicity was carried out using the Sulforhodamine B (SRB) assay on a 3T3 embryonic fibroblast mouse cell line. Phytochemical screening revealed the presence of tannins, alkaloids, flavonoids, steroids and saponins. Phenols and tannins were detected in the three extracts of water (H2O), methanol (MeOH), and methanol: dichloromethane (MeOH-DCM). The MeOH extract exhibited the highest TTC (0. 44 ± 0.01 mg TAE/g) as well as TPC (0.31 ± 0.05 mg GAE/g). In contrast, the MeOH-DCM (1:1) extract exhibited the highest TFC of 0.12 ± 0.01 mg QE/g. Flavonoid quantity was not detectable in the water extract. The MeOH extract demonstrated moderate antimicrobial activity against Candida albicans (12.0 ± 1.0 mm), Listeria monocytogenes (6.0 ± 3.0 mm), Enterococcus durans (6.0 ± 2.8 mm) and weak antimicrobial activity against Escherichia coli (4.0 ± 1.0 mm) and Shigella Sonnei (4.0 ± 2.6 mm). The MeOH-DCM extract demonstrated moderate antimicrobial activity against Candida albicans (10.0 ± 1.0 mm), Enterococcus durans (6.0 ± 1.7 mm) and weak antimicrobial activity against Listeria monocytogenes (5.0 ± 1.7 mm), Escherichia coli (3.0 ± 2.5 mm) and Shigella Sonnei (3.0 ± 1.4 mm). The water extract demonstrated moderate antimicrobial activity against Candida albicans (6.0 ± 1.0 mm) and weak antimicrobial activity against Listeria monocytogenes (4.0 ± 2.3 mm), Escherichia coli (4.0 ± 1.5 mm), Enterococcus durans (4.0 ± 1.8 mm) and Shigella Sonnei (3.0 ± 1.4 mm). Overall, the MeOH (12.0 ± 1.0 mm) and MeOH-DCM (10.0 ± 1.0 mm) extracts were active against the yeast isolate C. albicans. The H2O extract demonstrated weak antimicrobial activity (≤ 6.0 ± 1.0 mm) against Listeria monocytogenes, Enterococcus durans, Shigella Sonnei and Escherichia coli. The highest
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antimicrobial activity of the methanol extract (12.0 ± 1.0 mm and MIC ranging from 3.125 to 6.25 mg/mL) was recorded against C. albicans, indicating antifungal activity. Little to no cytotoxicity of the plant is reported against the 3T3 embryonic fibroblast mouse cell line. High tannin and phenolic contents present in the rhizome extracts together with the observed moderate antimicrobial activity supports the folklore use of the plant rhizome as a cure for stomach and throat complaints as well as an astringent in dysentery. However, the findings of this study suggest that the safety of the plant in traditional usage needs to be confirmed by further testing in vitro, in vivo and in clinical studies. Further studies could look into the characterization and identification of the bioactive compounds present in the rhizomes of H. abyssinica.
KEYWORDS: Acacia nigrences, Antimicrobial activity, Cytotoxicity, Hydnora abyssinica, Phytochemical analysis.