Evaluation of Antibacterial Activity and Phenolic Contents of Four Nigerian Medicinal Plants

Abstract

In this study, phenolic compounds and antimicrobial properties of four medicinal plants from Nigeria was investigated. The antibacterial properties and minimum inhibition concentration of Microdesmis puberula, Hypoestis verticillaris, Icacina tricantha, and Enterolobium cyclocarpum against 21 different bacteria was carried out using the disc diffusion assay. These plant extract were subjected to phytochemical screening by reverse phase HPLC (high pressure liquid chromatography) coupled with diode array detection and GC-MS (gas chromatography- mass spectrum). H. verticillaris had the most significant activity and showed inhibitory activity against most of the Gram-positive bacteria. However, M. puberula was only effective against the growth of Staphylococcus aureus and Enterobacter sakkai with inhibition zone of 8 mm. Furthermore, both I. tricantha and E. cyclocarpum only had antimicrobial effect on S. warneri with the inhibition zone of 12 and 13 mm, respectively. The results showed that M. puberula mostly contained 0.46 mg100 g^-1 dry sample quarcetin and H. verticillaris contained approximately 0.7 mg 100 g^-1 dry sample mangiferin and quarcetin. Moreover, both I. tricantha and E. cyclocarpum contain mostly quarcetin and rutin. According to GC-MS results, M. puberula contained thymol and methyl cinnamic acid and H. verticillaris contained methyl cinnamic acid and gallic acid. These plant extracts can be considered to be used in the cosmetic and food industries or even as a safe alternative to synthetic antimicrobial drugs.