Antibacterial secondary metabolites from Vernonia auriculifera Hiern (Asteraceae) against MDR phenotypes

Purification of the aerial parts of Vernonia auriculifera Hiern afforded steroids (1-2), flavonoids (3-5), and polyalcohol (6). Their structures were determined using spectral evidences as well as by comparison with reported data. Iodonitrotetrazolium chloride (INT) colorimetric assay was used to assess the antibacterial activity of the extract and isolates against 13 pathogenic strains. The crude extract showed strong antibacterial activity (MIC < 100 mu g/mL) against the tested bacterial strains. When combined with an efflux pump inhibitor phenylalanine beta naphthylamide (PA beta N), the inhibition potency of the extract was substantially enhanced with the lowest MIC value at 4 mu g/mL. Compounds 5 and 6 showed moderate activity (MIC < 100 mu g/mL) against 12/13 (92.3%), and 8/13 (61.5%) bacterial strains, respectively. A minimal bactericidal concentration (MBC)/minimal inhibitory concentration (MIC) ratio <= 4 indicated their bactericidal effect against Escherichia coli, Enterbacter aerogenes, Klebsiella pneumoniae, Providencia stuartii, Pseudomonas aeruginosa, and Staphylococcus aureus.

Automated summary

Extraction from the aerial parts of Vernonia auriculifera Hiern yielded compounds with antibacterial activity, with some showing strong inhibition against pathogenic strains. Efflux pump inhibitor was found to enhance the inhibitory potency of the extract, indicating the potential of these compounds as antibacterial agents.