Evaluation of GC × GC-TOF-MS untargeted metabolomics, cytotoxicity and antimicrobial activity of leaf extracts of Artemisia afra (Jacq.) purchased from three local vendors

Abstract

Objectives

As microorganisms are developing resistance to therapies, the search for potent antimicrobial compounds continues. The potential of detecting new compound(s) with antimicrobial activities from extracts of Artemisia afra, a South African plant frequently used for the treatment of diseases and widely traded in the market was explored. A. afra was purchased from three vendors. Methods: The dried leaf powder extracted separately with butanol, chloroform, and water were evaluated for cytotoxicity and antimicrobial activity using standard methods, and characterized for antimicrobial compounds using untargeted metabolomics. Results and Conclusion: All the extracts exhibited antibacterial activity. Butanol extract of vendor B sample was the most active against P. aeruginosa while the antibacterial activity of water extract of vendor A against S. aureus, E. coli, and E. faecalis was similar to butanol extract of vendor B. All other extracts were less cytotoxic than the chloroform extract of vendor B (LC₅₀ value = 414.56 ± 4.81 µg/mL). GC × GC-TOF-MS detected 436 compounds, 280 identifications were confirmed with 34 having known antimicrobial properties. The concentrations of compounds varied among the vendors’ samples with the highest in all samples and particularly in samples from vendor C (14.85 µg/mg) being Bicyclo[2.2.1]heptan-2-one 1,7,7-trimethyl-(1S)-, an antimicrobial compound. While two compounds were undetectable in vendor A sample, four were undetected in vendor C sample and eleven compounds in vendor B sample. The antibacterial activity of extracts could not be related to the metabolites variations and concentration. The A. afra species purchased from vendors from the traditional medicinal market showed antibacterial potential. To our knowledge, this was the first study to report the metabolomics of A. afra in respect to antimicrobial activities.