Evaluation of antibacterial and phytochemical properties of methanolic leaf and root bark extracts of Newbouldia leavis Seeman ex Bureau (Bignoniaceae)

Abstract

Methanol fraction of Newbouldia leavis root bark and leaf extract were analyzed in-vitro for their antibacterial and phytochemical activities. Spot test and gas chromatography-mass spectrometry (GC-MS) were used to determine the phytoconstituents of the extracts. The plant extracts were tested against three multi-resistant bacteria isolated from infected wound. The antibacterial activity of the plant extracts was evaluated against Pseudomonas aeruginosa, Staphylococcus aureus and Escherichia coli using agar well diffusion method. Broth dilution method was used to determine the minimum inhibitory concentration (MIC) and minimum bacteriocidal concentration (MBC). The extracts showed the presence of alkaloid, tannins, flavonoids, saponins, cardio-active glycosides, terpenoids, phenols and steroids. The GC-MS analysis showed the presence of 17 compounds in the leaf extract and 16 compounds in root bark extract. The two extracts have 7 compounds in common. The results of the zone of inhibition test showed that the root extract at the concentration of 50 and 100 mg/mL inhibited the growth of E. coli, P. aeruginosa and S. aureus while the leaf extract inhibited the growth of E. coli and S. aureus at the concentration of 25, 50 and 100 mg/mL and P. aeruginosa at 50 and 100 mg/mL. The MIC of the root bark extract against all the test bacteria was at 50 mg/mL while the MIC of leaf extract against E. coli and S. aureus was at 25 mg/mL and P. aeruginosa at 50 mg/mL. MBC of both extracts against the three test bacteria was at 100 mg/mL except root bark extract that has no MBC against P. aeruginosa. The study shows that methanol extract of the leaf and root-bark of Newbouldia leavis possess antibacterial activity and justified the traditional use of this plant in the treatment of wound and other bacterial infection.

Keywords: Antibacterial, phytochemical, Newbouldia leavis, broth dilution, Gas Chromatography-Mass Spectrometry