Phytochemical profiles and antimicrobial activity of Coleus lanuginosus (hochst. ex benth.) and Microglossa pyrifolia (Lam.) Kuntze extracts

Abstract

Introduction: Coleus lanuginosus and Microglossa pyrifolia are woody perennial herbs that are widely cultivated in Africa, Asia, and Australia. The use of crude extracts from leaves, stems and roots of these plants has been reported in traditional folklore medicine as a remedy for varied diseases. This study sought to investigate the phytochemical composition and evaluate the antimicrobial activities of the stem and leaf extracts of Coleus lanuginosus and Microglossa pyrifolia. Methods: the stem and leaf of both plants were collected from eastern Kenya, air-dried, and crushed into powder, and the crude extract was obtained using Soxhlet apparatus with aqueous and methanolic solvents. The antibacterial and antifungal activity was evaluated against gram-positive bacteria (Bacillus subtilis, Staphylococcus aureus) and gram-negative bacteria (Pseudomonas aeruginosa, Escherichia coli) and the fungus Candida albicans. Antibacterial and antifungal activity were evaluated by the disc diffusion method. The minimum inhibitory concentration (MIC) of the extracts was also determined. Results: qualitative and quantitative phytochemical screening was done on the two plants to establish the presence of biologically important secondary metabolites. Both methanolic and aqueous crude extracts of C. lanuginosus and M. pyrifolia demonstrated to possess antibacterial and antifungal activity against the selected microbes. The extracts showed minimum inhibitory concentration (MIC) activity against Bacillus subtilis, Staphylococcus aureus Pseudomonas aeruginosa and Escherichia coli ranging from 6.25mg-50mg/kg with M. pyrifera leaf extract resulting in the highest zones of inhibition. The phytochemical constituents identified were flavonoids, alkaloids, glycosides, phenols, saponins, steroids, and terpenoids, with alkaloids, glycosides, saponins, and steroids being the most abundant. Gas chromatography-mass spectrometry (GC-MS) analysis led to the identification of fifty-nine compounds with all the extracts containing at least two or more long-chain unsaturated fatty acids which have been linked to antimicrobial activity. Conclusion: in conclusion, C. lanuginosus and M. pyrifolia extracts have great potential as a source of novel antimicrobial and antifungal agents and possess a wide range of bioactive phytochemical compounds with the potential for ethnomedicinal use.