ABSTRACT

Background and Aim: The increasing prevalence of multidrug-resistant (MDR) foodborne bacteria has intensified the search for natural antibacterial agents with potential applications in food safety. Medicinal plants are rich sources of bioactive compounds, but the antibacterial potential of many plants traditionally used in Libya remains insufficiently characterized, particularly against MDR foodborne isolates. This study aimed to evaluate the in vitro antibacterial activity of extracts from 22 medicinal plant species against MDR bacteria isolated from foods of animal origin and to determine how the extraction solvent affects antibacterial efficacy.

Materials and Methods: Twenty-two medicinal plant species collected or purchased in Libya were extracted using methanol, petroleum ether, and ethyl acetate. The extracts were screened against five previously characterized MDR bacterial isolates: Escherichia coli EC 56 and EC 184, Staphylococcus aureus SA 121, Klebsiella pneumoniae KP 243, and Bacillus cereus BC 4. Antibacterial activity was initially assessed using agar well diffusion at 100 mg/mL. Extracts producing inhibition zones >11 mm were further evaluated by broth microdilution to determine the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC).

Results: Nineteen extracts derived from nine medicinal plant species exhibited antibacterial activity against at least one MDR isolate. Petroleum ether and ethyl acetate extracts generally produced greater antibacterial activity than methanol extracts. Cinnamomum verum demonstrated the strongest activity, with its ethyl acetate extract exhibiting an MIC of 0.78125 mg/mL against all five isolates and inhibition zones of 17.5–26.5 mm. Its petroleum ether extract showed an MIC of 0.78125 mg/mL against four isolates and 1.5625 mg/mL against E. coli EC 56. The petroleum ether extract of Syzygium aromaticum achieved an MIC of 0.78125 mg/mL against S. aureus SA 121 and B. cereus BC 4, whereas Thymus capitatus showed MIC values of 1.5625–6.25 mg/mL. MBC values were generally equal to or two-fold higher than the corresponding MIC values (MBC/MIC ≤2), indicating predominantly bactericidal activity. B. cereus BC 4 was the most susceptible isolate.

Conclusion: C. verum, S. aromaticum, and T. capitatus showed promising antibacterial activity against MDR foodborne bacteria. The superior performance of petroleum ether and ethyl acetate extracts highlights the importance of solvent selection and supports further phytochemical characterization of active compounds for potential development as natural antibacterial agents and food preservatives.

Keywords: antibacterial activity, foodborne bacteria, Libyan medicinal plants, medicinal plant extracts, minimum inhibitory concentration, multidrug resistance, natural antibacterial agents, solvent extraction.