Evaluation of in-vitro antibacterial and antifungal activities of crude extracts and solvent fractions of methanol extract of leaves of Ricinus communis Linn (Euphorbiaceae) against selected pathogens

Abstract

Background Impacts of infectious diseases are reduced due to development of antimicrobial agents. However, the effectiveness of the antimicrobial agents is reduced over time because of the emergence of antimicrobial resistance.To overcome these problems scholars have been searching for alternative medicines, particularly focusing on traditionally used medicinal plants. Ricinus communis Linn is used as a traditional treatment for bovine mastitis, wound infection, and other medicinal purposes. Moreover, the antimicrobial activity of Ricinus communis Linn leaf at crude extract level has been confirmed against human originated pathogens in the previous studies. The objective of the present study was to further evaluate the antimicrobial activities of Ricinus communis Linn leaf extracts and fractions. The Ricinus communis Linn leaves were macerated in absolute methanol and acetone solvents. The methanol crude extract was shown best antimicrobial activity and exposed to further fractionation via increasing polarity of solvents (n-hexane, chloroform, ethyl acetate, and aqueous). Test microorganisms included in the study were six laboratory reference bacteria (E. coli, S. aureus, S. agalactiae, K. pneumoniae, P. aeruginosa, and S. Pyogenes), two clinical isolate bacteria (E. coli and S. aureus), and Candida albicans. The agar well diffusion method was employed to determine antimicrobial activity. The minimum inhibitory concentrations (MIC) and minimum bactericidal/fungicidal concentrations (MBC/MFC) were determined through broth microdilution method. Results The results indicated that the best antimicrobial activity(based on zone of inhibition) for ethyl acetate fraction ranging from 14.67 mm (clinical E. coli) to 20.33 mm (S. aureus) at 400mg/ml however, n-hexane exhibited lowest antimicrobial activity. Among tested fractions, ethyl acetate fraction was produced lowest MIC values ranging from 1.5625mg/ml (S. aureus) to 16.67 mg/ml (Candida albicans). The ethyl acetate fraction showed bactericidal activity against all tested microorganisms. Conclusion Methanol extract of Ricinus communis Linn leaf exhibited better antimicrobial activity than acetone extract. Hence, ethyl acetate fraction of crude methanol extract exhibited best antimicrobial activity indicating its potential for development of antimicrobial products.