Richardia brasiliensis Collected in Southern-Benin: Phytochemical Screening, Antimicrobial Activity and Toxicity

Aims: The aim of this study is to evaluate the antimicrobial activity of the R. brasiliensis aerial part extracts collected in southern-Benin.

Methodology: The phytochemical screening was performed by a differential precipitation staining method. Aqueous and ethanolic extracts were made using conventional method with water and ethanol as solvent. The obtained extracts were used to evaluate their antimicrobial activity on Staphylococcus aureus strains isolated from skin infections and ten reference strains by the solid-medium diffusion method. The minimum inhibitory concentrations (MIC) and minimum bactericidal concentrations (MBC) were determined by the liquid macro-dilution method. The cytotoxic effect of the extracts was evaluated on Artemia salina larvae obtained by hatching.

Results: The phytochemical screening showed a strong presence of tannins, flavonoids, terpenes, steroids and a medium presence of alkaloids, anthocyanins and mucilage’s. The extraction yields vary according to the solvent: water (15.5%) and ethanol (10.30%). The two extracts variously (p<0.001) inhibited the growth of Staphylococcus aureus strains isolated from skin infections and four reference strains (Staphylococcus aureus ATCC29213, Pseudomonas aeruginosa ATCC27853, Proteus mirabilis A24974, Escherichia coli ATCC25922). However, there is no difference (p > 0.05) in inhibition of strains growth between 24h and 48h. The largest diameter (21±0.75 mm) of inhibition with the reference strains was obtained with P. aeruginosa by action of the aqueous extract. Regarding Staphylococcus aureus strains isolated from skin infections, the largest diameter of inhibition is about 19.25±2.75 mm obtained with strains isolated from ulcers. The average mics of 2.81 mg/ml and 2.08 mg/ml were obtained respectively for the aqueous and ethanolic extracts in the presence of the reference strains. The LC50 determination obtained using the regression line is 0.36 mg/ml for the aqueous extract and 1.16 mg/ml for the ethanolic extract.

Conclusion: The aqueous extract is more effective because of its action spectrum. This extract can be used for the development of a soap or ointment to fight against skin infections.