PHYTOCHEMICAL SCREENING, ANTIMYCOBACTERIAL AND ANTICANDIDAL ACTIVITIES OF CRUDE EXTRACTS AND FRACTIONS FROM VERNONIA GLABRA

Abstract

Vernonia glabra is used by Malawian traditional healers to treat a myriad of ailments including shingles, diabetes, diarrhoea, cough, wounds and gonorrhoea. This study evaluated phytoconstituents and the in vitro antimycobacterial and anticandidal 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 and anticandidal activities of dichloromethane (DCM) ethyl acetate (EtOAc) and methanol (MeOH) crude extracts and fractions from the roots, leaves and stem. 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 root fraction exhibited the highestantimycobacterial activity against Mycobacterium tuberculosis H37Rv. The 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 of3.13 μg/mL and 3.88 μg/mL, respectively. The EtOAc root crude extract showed the best Total activity (TA) of 13174 mL/g. Both EtOAc (leaf) and MeOH (stem) crude extracts exhibited activity against Candida albicans with a MIC value of 625.0 μg/mL, and IC50 values of 717.9 μg/mL and 1025 μg/mL, respectively, whereas, fluconazole, which was used as a standard, showed MIC and IC50 values of 12.5 μg/mL and 12.71 μg/mL, respectively. GC-MS and FTIR analyses of the most active EtOAc fraction revealed the presence of hexadecenoic acid, methyl ester (0.39%), diisooctyl phthalate (24.56%) and octacosane (51.12%). The identified compounds are reported in the literature to possess antimicrobial and anticancer activities. Comparison of the hill slope (HS) values of the dose-response curves of the fraction (-1.005) and its crude extract (-1.322) showed that repeated fractionation improved the activity. Therefore, this study showed that the roots of Vernonia glabra present a potential source of new lead for antimycobacterial drugs.