Phytoconstituents and Antimycobacterial Activities of Root Extracts and Fractions from Vernonia glabra, (Steetz) Vatke

Abstract

Vernonia glabra is used by Malawian traditional healers to treat a myriad of ailments including shingles, diabetes, dysentery, diarrhoea, cough, wounds, gonorrhoea, and gastrointestinal problems. This study evaluated phytoconstituents and the in vitro antimycobacterial activities of the crude extracts and fractions from roots of Vernonia glabra. Agar disk diffusion and modified broth microdilution assays were used to determine the antimycobacterial activities of dichloromethane (DCM) and ethyl acetate (EtOAc) crude extracts and fractions from the roots. Gas chromatography-mass spectrometry (GC-MS) and Fourier-transform infrared spectroscopy (FTIR) analyses were used to characterise the major compounds in the crude extracts and fractions. The EtOAc fraction exhibited the highest antimycobacterial activity against Mycobacterium tuberculosis H37Rv. The EtOAc fraction achieved a minimum inhibitory concentration (MIC) of 4.88 μg/mL and a half-maximal inhibitory concentration (IC50) value of 38.37 μg/mL, whereas gentamycin, a standard drug, achieved MIC and IC50 values of 3.13 μg/mL and 3.88 μg/mL, respectively. GC-MS and FTIR analyses of the EtOAc fractions revealed the presence of hexadecenoic acid, methyl ester (0.39%), diisooctyl phthalate (24.56%), oxalic acid, allyl undecyl ester (4.66%), bis(2-ethylhexylphthalate) (5.41%), octacosane (51.12%), tetradecane (12.63%), phenol, 3,5-bis(1,1-dimethylethyl) (0.07%), and 2-hydroxy-4-methylbenzaldehyde (6.47%). The identified compounds are reported in the literature to possess antimicrobial and anticancer activities. It was evident from the comparison of the hill slope (HS) values of the dose-response curves of the fraction (−1.005) and its crude extract (−1.322) that repeated fractionation improved the activity. Therefore, this study showed that the roots of Vernonia glabra present a potential source of new leads for antimycobacterial drugs.