<i>In vitro</i> Antimicrobial Activity of Homonataloin A/B and Homonataloside Against Pathogenic Microorganisms

Abstract

In the past few decades, antimicrobial drugs are losing their effectiveness due to the evolution of pathogen resistance. Thus, there is a continuing search for natural products that have potential to lead to more effective and less toxic alternative antimicrobial drugs. In this context, two anthrones (homonataloin A/B and homonataloside) were isolated from the leaf latex of Aloe citrina Carter & Brandham by preparative thin layer chromatography over silica gel. The latex and its two constituents were tested for their antimicrobial activities against 20 bacterial and 4 fungal strains using disc diffusion method. Both the latex and isolated compounds were found to possess a broad spectrum of antimicrobial activity against Grampositive and Gram-negative bacteria as well as fungal strains. Broth dilution method was used to determine the minimum inhibitory concentration (MIC) of each of the test substances. Homonataloin A/B was found to exhibit good activity against Staphylococcus aureus and all Salmonella spp. tested with MIC value of 25 μg/ml, whilst the activity of homonataloside (MIC = 25 μg/ml) was highest against Vibrio cholerae strains. Among the fungal strains tested, Candida albicans was the most susceptible organism to the latex and the isolated compounds. By and large the activity of the latex was either comparable or better than the isolated compounds against all bacterial strains tested indicating the possible presence of synergy among the isolated compounds or the presence of minor compounds in the latex with strong antibacterial effect. These findings support the traditional uses of the plant for the treatment of various infectious diseases and wound.

Keywords: Aloe citrina, Homonataloin A/B, Homonataloside, Antimicrobial Activity, Disc Diffusion