Comparative analysis of Annona muricata Linn (soursop) leaf and fruit extracts against selected pathogens

Abstract

Multidrug resistance to antibiotics has necessitated the need for natural products which are alternative method of antimicrobial stewardship. The use of plants, which provide safe and cost effective remedies can be properly harnessed and regulated provided there are scientific-based evidences. This study compared the bioactivity of soursop leaf and fruit extracts against selected pathogens. Extract yield as well as analysis of inherent phytochemicals of soursop fruit and leaf were estimated using standard methods. Agar well diffusion method was used for antimicrobial screening and minimum inhibitory concentration (MIC) against test isolates. 24g and 33g extract was obtained from 60g dried soursop leaves and fruits, resulting in approximately 40% and 55% yield, respectively, using methanol as extraction solvent.  Qualitatively, saponins, tannins, flavonoids, terpenoids, alkaloids and phenols were present in both samples however, cardiac glycosides, anthraquinones and steroid was absent in the fruit.  Quantities of the compounds ranged from 43 to 940 mg/100g (leaves) and 18 to 560 mg/100g (fruit), respectively. The fruit extract inhibited the growth of Staphylococcus aureus (15±0.15 mm), Pseudomonas aeruginosa (20±0.12 mm), Bacillus alvei (30±0.47 mm) and Escherichia coli (12±0.52 mm) while the leaf extract inhibited only S. aureus (14±0.91 mm) and B. alvei (15±0.76 mm).  200 mg/mL was the minimum inhibitory concentration of the extracts against S. aureus and B. alvei and E. coli. Conclusively, the findings of this study indicated that soursop leaf and fruit have varied phytochemicals. The fruit extract however showed higher antimicrobial inhibitory effects when compared to the leaf extract.