Phytochemistry and Antimicrobial Properties of Gmelina arborea (Verberaceae) Ethanolic Leaf Extract and its Secondary Metabolites
Authors: CO Akalezi 
Published: January 2024

The aim of this study was to determine the antimicrobial potential of Gmelina arborea ethanolic leaf extract which is used in traditional medicine for treating different ailments such as hallucinations, piles, abdominal pains, burning sensation, diabetes and fever. It is also intended to study its acidic, basic and neutral metabolites with a view to identify the phytochemical compounds responsible for the observed antimicrobial properties. Phytochemical screening was carried out on the airdried ethanolic leaf extract and its secondary metabolites in the Research Laboratory of Phytochemistry/ Chromatography, N4 Alaenyi Street, Owerri, Imo State, Nigeria. The antimicrobial study was carried out using the Agar disc diffusion method and determination of Minimal Inhibitory Concentration (MIC) in the department of Microbiology, Federal Medical Centre, Owerri, Imo State, Nigeria. The ethanol leaf extract and its secondary metabolites (acidic, basic and neutral) were prepared and assayed for antimicrobial activities. The test microorganisms used were Streptococcus spp, Staphylococcus aureus, Salmonella spp, Escherichia coli and Coliform bacilli. Inhibition zone diameter was used as a measure of the antimicrobial activity. The results of the antimicrobial screening of the crude extract and metabolites showed that the crude extract, acidic and neutral metabolites possessed antimicrobial activity to various extents against the microorganisms tested whereas the basic metabolite showed no activity at all. The results showed that the crude extract exhibited its greatest activity against Streptococcus spp, Staphylococcus aureus and Escherichia coli with inhibition diameter of 20 mm at 1.0 mg/ml and MIC of 0.5 mg/ml. The least activity was against Salmonella spp with inhibition zone diameter of 15 mm and MIC of 0.5 mg/ml. The acidic metabolite exhibited its greatest activity against Escherichia coli with inhibition zone diameter of 35 mm at 1.0 mg/ ml and MIC of 0.25 mg/ml. The least activity was against Staphylococcus aureus and Salmonella spp with inhibition zone diameter of 25 mm at 1.0 mg/ml and MIC of 0.5 mg/ml respectively. The neutral metabolite exhibited its greatest activity against Salmonella spp and Coliform bacilli with inhibition zone diameter of 30 mm at 1.0 mg/ml and MIC of 0.5 mg/ml. The least activity was against Staphylococcus aureus with inhibition zone diameter of 22 mm at 1.0 mg/ml and MIC of 0.5 mg/ml. The phytochemical screening results showed the presence of alkaloids, flavonoids, tannins, saponins, cyanogenic glycosides, steroids, carbonyl compounds and carbohydrates. Saponins, carbonyl compounds and carbohydrates were shown to be much higher in concentration than other phytochemicals. The results obtained in this study confirm the antimicrobial properties of Gmelina arborea leaf extract and suggest that this property resides in the acidic and neutral metabolites since the basic metabolite showed no activity at all. The study supports the use of this plant in folk medicine for treatment of ailments such as stomach disorders, healing of wounds, burning sensation and fever.