In vitro antimicrobial and larvicidal properties of wild Ricinus communis L. in Mauritius

Objective: To explore the phytochemical and antimicrobial activities as well as the insecticidal properties of the different sections of Ricinus communis (castor) plant in Mauritius. Methods: Qualitative and quantitative methods were used for the determination of phytochemicals in the crude leaves, pericarp, seeds, bark and root extracts obtained by using polar and non-polar solvents. The disc diffusion and micro-dilution methods were used to evaluate the antimicrobial activities of the crude solvent extracts against 13 microorganisms. The insecticidal properties of the crude extracts on larvae of Bactrocera zonata (Diptera: Tephritidae), which caused important economic losses to local fruits were also investigated. Results: All the extracts from the different parts of the plant showed antimicrobial activity against most tested microorganisms. The polar solvents' extracts of the fully mature parts of the castor plant were active against the Pseudomonas aeruginosa (ATCC 27853), Escherichia coli (E. coli) (ATCC 25922), E. coli (0145:H28 Acc. No. CP006027.1) with inhibition zones ranging from 16 mm to 19 mm and against Bacillus cereus (ATCC 11778) (B. cereus), Listeria innocua (ATCC 33090) (L. innocua). Lowest microbial inhibitory concentration was recorded for B. cereus, L. innocua, Staphylococcus aureus (ATCC 29213), E. coli (ATCC 25922) and Proteus mirabilis strain (NCTC 11938) with value of 3.2 mg/mL. The most active extract against both Gram-negative and Grampositive bacteria was extracted from the fully mature pericarps and it was the most active against E. coli (ATCC 25922), B. cereus, L. innocua and Staphylococcus aureus (ATCC 29213). In addition, the extracts obtained by using polar solvent and fully mature leaves demonstrated the strongest larvicidal activity against Bactrocera zonata (100%). Conclusions: Ricinus communis (castor) plant extracts possess larvicidal properties providing an effective eco-friendly control for fruit flies. The antimicrobial results justify the use of this plant in traditional medicine and the practice of supplementing decoctions/ concoctions with conventional antibiotics.