Tehran University of Medical Sciences Iranian Journal of Microbiology 2008-3289 17 1 2025 02 05 171 179 Fatemeh Hajmoradi Department of Biology, Faculty of Science, Payame Noor University, Tehran, Iran Hamed Fathi Department of Biology, Faculty of Science, Payame Noor University, Tehran, Iran; Pharmaceutical Sciences Research Center, Hemoglobinopathy Institute, Mazandaran University of Medical Sciences, Sari, Iran Foozieh Moghadami Department of Biology, Faculty of Science, Payame Noor University, Tehran, Iran 2024 08 23 2025 01 06 Background and Objectives: Senecio vulgaris L., a member of the Asteraceae family, has been widely employed in traditional Iranian herbal practices for centuries. This research seeks to analyze and compare the essential oil compositions and antibacterial characteristics of two distinct populations of S. vulgaris. Materials and Methods: Essential oils were obtained from the above-ground parts of these populations through hydrodistillation, and their chemical constituents were examined using gas chromatography-mass spectrometry. The antibacterial effectiveness of the essential oils against both Gram-positive and Gram-negative bacteria was evaluated employing the agar well diffusion technique. Results: Monoterpene hydrocarbons were found to be dominated in both populations, with Humulene epoxide II being the primary constituent, constituting 17.87% in the first population and 21.55% in the second one. The agar-well diffusion method revealed significant antibacterial effects of the S. vulgaris essential oils. The findings indicated that the essential oil displayed heightened activity against Escherichia coli in both populations. Furthermore, minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) tests indicated that Pseudomonas aeruginosa with concentrations of 400 µg/mL for both tests, was the most susceptible bacteria, while Streptococcus pyogenes with MIC = 800 and MBC>800 µg/mL was the most resistant in both populations of S. vulgaris. Conclusion: This research highlights the significance of S. vulgaris as a valuable reservoir of monoterpene-rich oil exhibiting robust antibacterial characteristics, suggesting its potential use in the development of novel and naturally derived therapeutics for bacterial diseases. https://ijm.tums.ac.ir/index.php/ijm/article/view/5002 https://ijm.tums.ac.ir/index.php/ijm/article/download/5002/1755