Gas chromatography - mass spectrometry characterization and antibacterial activity of stem-bark extracts of Dacryodes edulis (African pear)

This study investigates the antibacterial activities of the stem bark extract of Dacryodes edulis. The aim of the study was to deduce the potency of the crude extracts and their metabolites from stem-barks of Dacryodes edulis on drug-resistant microbial pathogen (s). The stem bark of the plant was extracted with five solvents of different polarities. While extraction with hexane, dichloromethane, ethyl acetate, and methanol were done using a soxhlet extractor, aqueous extract was obtained by soaking 250 g of powdered samples in 200ml of distilled water for 18 hours The five plant extracts were subjected to phytochemical screening that revealed the presence of alkaloids, flavonoids, carbohydrates, tannins, saponin, steroids, and triterpenes. The bioactivity of the extracts at varying concentrations of 250 mg/mL, 200mg/mL, 150 mg/mL, 100 mg/mL, 50 mg/mL and 25 mg/mL were determined. Based on the result of the bioassay, the most active extracts were partitioned into acidic, basic, and neutral metabolites and the bioactivity tests were repeated on the metabolites. The extracts elicited antibacterial activity against all the strains tested zones of inhibition ranging between 1 mm to 36 mm. The bactericidal effects of the extracts on all the microorganisms tested were positive at 250 mg/mL and 200 mg/mL. Also, the acidic, basic, and neutral metabolites of the Methanol and the Ethylacetate extracts exhibited bactericidal effects at 250 mg/mL. At 200 mg/mL, all the six samples except the neutral metabolite of the methanol extract (which was only effective against Staphylococcus Aureus, Salmonella typhi, and Salmonella Paratyphli) exhibited antibacterial activity. The gas chromatography-mass spectrometry (gc-ms) spectra revealed 4-dehydroxy-N- (4, 5-methylenedioxy-2-nitrobenzylidene) tyramine and1, 2bis (2-methyl propyl) benzene dicarboxylateas the most abundant compound in the basic metabolites of ethyl acetate and methanol extracts respectively. The most active metabolites were basic metabolites of ethyl acetate and methanol extracts. While the basic metabolites of ethyl acetate contain mostly alkaloids; the basic metabolites of methanol contain mostly terpenoids. These active metabolites possess antibacterial activity against Staphylococcus aureus and other pathogens tested.