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

Abstract

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 µg/mL) against the tested bacterial strains. When combined with an efflux pump inhibitor phenylalanine beta naphthylamide (PAβN), the inhibition potency of the extract was substantially enhanced with the lowest MIC value at 4 µg/mL. Compounds 5 and 6 showed moderate activity (MIC < 100 µg/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.

Graphical abstract

Keywords:

• Vernonia auriculifera
• Asteraceae
• multidrug resistant bacteria
• efflux pump
• antibacterial activities

Acknowledgements

The authors are grateful to the Cameroon National Herbarium for plant identification. We acknowledged the financial support of the International Science Programme (ISP) through the KEN-02 project. Special thanks to Dr. G.T.M. Bitchagno for valuable discussions.

Disclosure statement

The authors declare that they have no competing interest.