Isolation and characterization of antimicrobial and anti-inflammatory triterpenoids from the acetone extract of Grewia flava DC. (Malvaceae) roots

Abstract

Grewia flava root acetone extracts were assessed for antimicrobial activity against a range of pathogenic microorganisms using the broth microdilution and bioautography assays. Cytotoxicity against human dermal fibroblast (HDF) and bovine dermis (BD) cell lines was also investigated. Solvent-solvent fractionation was carried out on the acetone extract to yield fractions of different polarities. Bioautograms from fractions showed four antimicrobial compounds in the carbon tetrachloride fraction, with activity against Escherichia coli. Two compounds from carbon tetrachloride, hexane and butanol fractions were active against Candida albicans, Bacillus cereus, Klebsiella pneumoniae and Escherichia coli. The aqueous fraction had the lowest minimum inhibitory concentration (MIC) values of 40 µg/ml against Cryptococcus neoformans, Staphylococcus aureus, Klebsiella pneumoniae and Pseudomonas aeruginosa. Two triterpenoid compounds, namely taraxerol and lupeol, were isolated and had potent antimicrobial activity. Lupeol had better antimicrobial activity than vancomycin (control drug) with MIC of 10 µg/ml against Mycobacterium smegmatis, Mycoplasma hominis and Escherichia coli. Both taraxerol and lupeol exhibited better anti-inflammatory activity than quercetin (positive control) in the soybean lipoxygenase (15-LOX) inhibition assay and by inhibiting nitric oxide release from RAW264.7 macrophages. Although fractions and isolated compounds exhibited potent antimicrobial, antioxidant and anti-inflammatory activity, there is a need to explore the modes of action thereof. The study supports the use of the plant species in the treatment and management of various microbial infections posing danger to human health.