Phytochemical Analysis, In vitro Antibacterial Activity and Rate of Kill of Different Fractions of Dacryodes edulis Leaf

Dacryodes edulis is a fruit tree attaining a height of 18–40 meters mostly grown around the house and rarely in the forest. It has a relatively short trunk and a deep, dense crown and it is native to Africa hence often called African pear. The leaves are a compound with 5-8 pairs of leaflets. Acetone extract/solvent fractions of the leaves of Dacryodes edulis were used. The in vitro antibacterial activities and rate of kill of different fractions were investigated. The phytochemical screening was done by some chemical tests, antibacterial activity by agar well diffusion method and rate of kill was carried out on S. aureus and E. coli organisms. The fractions exhibited antibacterial activities with zones of inhibition ranged between 20 and 30 mm by Aqueous (AQU) fraction while Dichloromethane (DCM) fraction ranged between 22 and 32 mm. The standard antibiotics, streptomycin ranged between 10 and 20 mm and ampicillin between 11 and 27 mm. The Minimum Inhibitory Concentration (MIC) and Minimum Bactericidal Concentration (MBC) of both fractions had range values between 0.78 and 6.25 mg/mL. The phytochemical screening revealed the presence of alkaloids, tannins, saponins, flavonoids, terpenoid and glycoside. Overall, the two fractions had better activities than the standard antibiotics used. 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. The AQU fraction killed 100% of Escherichia coli and Staphylococcus aureus cells at concentration of 4.68 mg/mL (3 X MIC) within 120 min while DCM fraction killed 100% of Escherichia coli cells within 90 min at a concentration of 4.68 mg/mL and killed 100% of S. aureus cells within 120 min at a concentration of 3.12 mg/mL (2X MIC). In conclusion, D. edulis leaf fraction has a broad spectrum antibacterial activity, with the AQU and DCM fractions being bactericidal as exemplified by the killing rate and MIC index of 2 (ratio of MBC/MIC) for both fractions.