In vitro antimicrobial activities of anthrones from the leaf latex of Aloe sinana Reynolds

Abstract

Background: Aloe sinana Reynolds is endemic to Ethiopia where its leaf latex is traditionally used in and around the town of Debre Sina and other central highlands of the country for the treatment of various illnesses, including wound, snake bite and malaria. However, despite its use in traditional medicine, to date, there appears to have been no chemical or biological studies published on this plant. Aim: The aim of this study was to investigate the leaf latex of A. sinana for its antibacterial and antifungal activities, and to isolate and characterise the compounds that are responsible for the antimicrobial effect of the latex. Materials and Methods: The latex was extracted with methanol. Isolation of compounds was achieved by repeated preparative TLC, and spectroscopic techniques including 1H, 13C‑NMR and MS were used for characterisation of the isolated compounds. Antimicrobial activity tests were performed against 21 bacterial and 4 fungal pathogens using the disc diffusion method. Results and Conclusion: Three compounds isolated from the leaf latex were identified as the anthrones, aloin, aloinoside and microdontin. Among the isolated compounds, aloinoside and microdontin were found to possess comparable activity (MIC 5 μg/ml) with that of ciprofloxacin against several Gram‑negative bacterial strains and Staphylococcus aureus. Additionally, microdontin showed potent and comparable activity with the standard antifungal drug griseofulvin against Penicillum spp. These findings support the traditional uses of the plant for the treatment of various infections and wound. Key words: Aloe sinana, anthrones, antibacterial, antifungal, disc diffusion, latex