Lack of Antibacterial Activity in the Ayurvedic Plants Aconitum heterophyllum, Tephrosia purpurea, Tinospora cordifolia and Swertia chirayita

Background: The global rise of antimicrobial resistance (AMR) has intensified the search for alternative therapeutic agents derived from natural sources. This study investigated the antibacterial potential of four Ayurvedic medicinal plants Aconitum heterophyllum, Tephrosia purpurea, Tinospora cordifolia, and Swertia chirayita. Traditionally, these plants have been used in the management of various infectious diseases. Objectives: The ability for extracts of these pants to inhibit a panel of different bacterial pathogens was assessed. The bacteria included in the study were Staphylococcus aureus, methicillin-resistant S. aureus (MRSA), Escherichia coli, extended-spectrum β-lactamase (ESBL) E. coli, Klebsiella pneumoniae, ESBL K. pneumoniae, Bacillus cereus, Shigella sonnei, Shigella flexneri, and Salmonella typhimurium. Materials and Methods: Plants were extracted with water, methanol or ethyl acetate and their antibacterial activities evaluated using disc diffusion and broth microdilution assays. Artemia franciscana lethality assays were used to measure extract toxicity, whilst LC-MS analysis was conducted on the plant extracts to identify and characterise their chemical constituents, which may explain the findings arising from the antibacterial experiments. Results: There was no detectable antibacterial activity for any of the plant extracts tested against the selected bacterial strains. Each of the extracts were non-toxic in the Artemia franciscana lethality assay. LC-MS analysis revealed the presence of alkaloids, flavonoids, terpenoids, and other secondary metabolites within the extracts. Conclusion: The lack of activity may be due to the poor quality or potency of the plant materials obtained from commercial suppliers, low concentrations of active constituents, solvent limitations, or possible synergistic effects lost in crude extracts. Further studies using authenticated plant materials from different suppliers, optimised extraction and testing protocols are recommended to more rigorously evaluate their antibacterial potential.