Antimicrobial assessment and scanning electron microscopy analysis of sesquiterpene lactones isolated from the leaves of Inula racemosa Hook. f.

Natural products serve as a vital reservoir of structurally diverse bioactive molecules that provide a foundation for drug discovery across major therapeutic areas, including inflammation, cancer, neurodegeneration, and infectious diseases. The rapid rise of antimicrobial resistance (AMR) increases the demand for novel antibacterial agents, particularly from natural sources. In the present study, we investigated the antimicrobial potential of sesquiterpene lactones obtained from the plant Inula racemosa against a panel of WHO priority pathogens, including Gram-positive (Staphylococcus aureus and Methicillin-resistant S. aureus-MRSA) and Gram-negative (Acinetobacter baumannii and Escherichia coli) pathogens using the broth microdilution method. The analysis revealed that all six compounds have potential antibacterial efficacy; however, Compound 1 and 2 exhibited broader inhibitory effects than the other four molecules at the various tested concentrations. Furthermore, ultrastructural analysis by scanning electron microscopy (SEM) revealed extensive cellular damage, membrane disruption, elongation, and lysis in treated pathogens (MRSA, A. baumannii, and E. coli) following treatment with Compound 1 and 2. Collectively, these results underline the potential of sesquiterpene lactones as promising antimicrobial agents and position them as an inspiring natural scaffold for the development of next-generation antimicrobial agents.