Crude Drug Analysis, Antimicrobial and Larvicidal Screening of the Methanolic Leaf Extract of Cestrum nocturnum L. (Fam. Solanaceae)

Crude leaves of Cestrum nocturnum L. (Fam. Solanacease) were analyzed for their total extractives, ash and moisture content to characterize its physicochemical properties. Phytochemical analysis of the crude C. nocturnum resulted in the isolation of tannins, glycosides, alkaloids, steroidal saponins, sapogenins and flavonoids. Further separation of the methanolic leaf extract was done through liquid-liquid fractionation using five solvents with varying polarity namely, hexane, chloroform, ethyl acetate, butanol and water [1]. Thin layer chromatography and phytochemical screening were conducted to identify the secondary metabolites present in each fraction and subsequently, antimicrobial assay through paper disk diffusion method was tested against Staphylococcus aureus and Escherichia coli. The ethyl acetate fraction showed marked antimicrobial activity against the two bacterial strains with zones of inhibition ranged from 11 mm to 22 mm. This fraction was subjected to bioautography using chloroform:diethyl ether (2:1) identified as the optimum solvent system which was able to separate 8 distinct spots for both trials under different detection methods. The result showed no measurable zones of inhibition observed in any of the separated bands. The methanolic leaf extract was screened for its larvicidal activity according to WHO Communicable Disease Control Prevention and Eradication-WHO Pesticide Evaluation Scheme. All replicates of the sample from highest concentration (1 g/140mL; 100%) to lowest concentration (250 mg/140mL; 25%) had caused 100% mortality against third instar larvae of Aedes aegypti in 24 hours [2]. It is recommended to dilute the concentration of the sample to lower than 250 mg/140mL to determine the LC₅₀ of the methanolic extract of C. nocturnum. References: [1] Khan M, et al. (2011) African J Microbiol Res, 5: 613. [2] World Health Organization (2005) Guidelines for laboratory and field testing of mosquito larvicides.