The present study focused on the evaluation of the antimicrobial activity and antifungal of chemical constituents isolated from the roots of Vernonia guineensis, a plant of the family Asteraceae. Vernonia guineensis is used in traditional pharmacopoeia as aphrodisiacs, anti-dysenteric, purgative, anti-gastritis, antimalarial, anti-asthenic, febrifuge, anti-icteric. The chemical study of the CH₂Cl₂-CH₃OH mixture extract (1:1) led to the isolation of five compounds: Betulinic acid (1); alphitolic acid (2); β-sitosterol 3-O-β-D-glucopyranoside (3); scoparone (4); Quercetin-3-O-β-galactoside or isoquercetin (5). Betulinic acid (1), alphitolic acid (2) and scoparone (4) were isolated from Vernonia guineensis for the first time. The structures of the isolated compounds were elucidated based on spectroscopic analysis and comparison of their spectral data with those reported in the literature. The results of the antimicrobial tests on the 11 bacterial strains tested showed that the compounds (2) and (3) were active on most the bacterial strains tested, whereas the compound (1) was active on 4 of the 11 bacterial strains. Tested with an inhibition diameter ranging from 7 to 8 mm, while the compound (5) acted only on 1 bacterial strain. On the other hand, the compounds (2) and (3) tested showed a strong inhibition on Staphylococcus aureus ATCC BAA 977, a moderate inhibition on Staphylococcus aureus ATCC 29213, a weak inhibition on Aerococcus viridans ATCC 11563 and a moderate inhibition on Enterococcus faecalis ATCC 51299. The MIC (Minimal Inhibitory Concentration), CMB (Concentration Minimal Bactericidal) and CMB/MIC ratios of compounds (2) and (3) have revealed the highest antibacterial potency. However, the MICs of the compound (2) vary from 312.5 to 2500 μg/mL with the smallest value (312.5 μg/mL) observed against Staphylococcus aureus ATCC BAA 977, whereas the compound (3) MICs vary from 312.5 to 5000 μg/mL with the lowest value (312.5 μg/mL) observed against Staphylococcus aureus ATCC BAA 977. The calculation of the CMB/MIC ratio revealed that compounds (2) and (3) had a bactericidal activity (CMB/MIC<4). This bactericide could justify their use in herbal medicine against bacterial infections.

Keywords: Antimicrobial Activities; Asteraceae; Secondary Metabolites; Vernonia guineensis ;