Investigations into Antibacterial, Phytochemical and Antioxidant Properties of Vitellaria paradoxa (Gaertn.) Stem Bark Extracts

Abstract

This study investigated the antibacterial potentials and mechanisms of action of crude extract and fractions from stem bark of Vitellaria paradoxa on susceptible bacterial isolates. It also assessed the phytochemical constituents and antioxidant properties of the plant. This was with a view to tackling problem of multidrug resistance development by microorganisms. The stem bark of V. paradoxa was harvested from Ijagbo, Kwara State, Nigeria, in the month of April, 2016. The plant sample was oven dried at 40°C using hot-air oven and ground into fine powder. The powdered sample was cold extracted using methanol and sterile distilled water in ratio 3:2 (v/v). The mixture obtained was concentrated in vacuo using a rotary evaporator and then lyophilized. The crude extract collected was screened for antimicrobial, phytochemical and antioxidant properties. The crude extract was later partitioned into fractions using different organic solvents in the order of their polarity. The antimicrobial potentials of the various solvent fractions were determined using agar-well diffusion method. The active fractions were further partially purified by combination of thin layer and column chromatography. The rate of killing, protein, nucleotide and potassium ions leakages of the active fractions were determined using Staphylococcus aureus and Escherichia coli as representatives of Gram positive and Gram negative bacteria respectively. The most active partially purified fraction was analysed using GC-MS. Phytochemical screening of the extract revealed the presence of alkaloids, flavonoids, saponins, tannins, reducing sugar and cardiac glycosides. The minimum inhibitory concentrations of the crude extract ranged between 0.545 mg/mL and 2.187 mg/mL while those of aqueous, butanol and ethylacetate fractions ranged between 0.31 mg/mL and 5.00 mg/mL, 0.31 mg/mL and 2.50 mg/mL and 0.31 mg/mL and 2.50 mg/mL respectively. The time kill assay showed that the percentage of the cells killed increased with increasing concentrations of the fractions, as well as, contact time intervals. Leakages of protein, potassium ions and nucleotides followed the same trend observed for killing rate. Vitellaria paradoxa extract exhibited 50% inhibition of DPPH free radicals at 0.008777 mg/mL, whereas ascorbic acid used as standard had IC50 of 0.078777 mg/mL. The major active constituent of the purified sample was identified as 14-methylhexadecanoic acid. The study concluded that V. paradoxa stem bark extract possessed antioxidant properties and exhibited appreciable antimicrobial activities against the test pathogens.