Exploring the antimicrobial efficacy of methanolic leaf extracts from cassia species against common pathogens

Abstract

The overuse of synthetic antibiotics has led to antibiotic resistance, prompting a new focus on plant-derived compounds for the development of new antimicrobial agents. This study investigates the antimicrobial properties of methanolic leaf extracts of five species of Cassia, C. tora, C. alata, C. occidentalis, C. absus and C. sophera against four common pathogens, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Candida albicans. Cassia species were selected based on their traditional use in Sri Lankan Ayurvedic medicine. The antimicrobial properties of the extracts were evaluated using the disc diffusion method of antimicrobial susceptibility testing and the minimum inhibitory concentration. In addition to antimicrobial testing, a preliminary phytochemical analysis of the extracts was undertaken to determine the presence of alkaloids, phenolics, tannins, and flavonoids. All extracts showed remarkable antimicrobial properties, with C. alata and C. tora showing the most significant zones of inhibition. Zones of inhibition for S. aureus were particularly evident, with C. alata showing a maximum zone inhibition of 16.22±0.04 mm. C. tora showed a zone of inhibition of 11.81±0.02 mm against E. coli, while C. alata showed 9.57±0.06 mm. Other Cassia species also showed remarkable activity across the tested pathogens, For C. albicans, all extracts proved their antifungal capabilities but required greater doses for efficacy and produced smaller inhibition zones compared to bacteria. In the reported MIC values, C. alata and C. tora consistently outperformed other Cassia species, demonstrating the lowest MIC values against the tested pathogens. The phytochemical analysis revealed that leaf extracts contain alkaloids, phenols, tannins and flavonoids, all known for their antimicrobial properties. The combined action of these components likely boosts the overall antimicrobial activity of Cassia leaf extracts, emphasizing their potential as a source of new antimicrobial agents for medicinal applications.