Screening of Antibacterial Activity of Selected Medicinal Plant Extracts Against Foodborne Pathogenic Bacteria

Medicinal plants have long served as a source of therapeutic agents in Libya and worldwide. This study investigated the in vitro antibacterial activity of twenty-two medicinal plant species against a panel of pathogenic bacteria previously isolated from food of animal origin in Libya. Plant materials were collected or purchased from different regions of Libya and extracted using three solvents of varying polarity: methanol, petroleum ether, and ethyl acetate. The extracts were screened for antibacterial activity against Escherichia coli (EC 56, EC 184), Staphylococcus aureus (SA 121), Klebsiella pneumoniae (KP 243), and Bacillus cereus (BC 4) using the agar well diffusion method. Extracts showing inhibition zones >11 mm were further evaluated for minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) using the broth microdilution method. Initial screening revealed that extracts from Thymus capitatus, Punica granatum, Syzygium aromaticum, Cinnamomum verum, Rosmarinus officinalis, and Myrtus communis exhibited notable antibacterial activity. The strongest effects were observed with petroleum ether and ethyl acetate extracts. Extracts of C. verum (R2, R3) and S. aromaticum (P2) showed the lowest MIC values, reaching 1.875 mg/mL against S. aureus (SA 121) and B. cereus (BC 4). MBC values were generally one- to two-fold higher than MIC values, indicating predominantly bactericidal effects. B. cereus (BC 4) was the most susceptible organism, whereas most extracts showed limited or no activity against E. coli strains. These findings confirm the strong antibacterial potential of several medicinal plants, particularly C. verum (cinnamon), S. aromaticum (clove), and T. capitatus (thyme). The results support their traditional use and highlight their potential as sources of natural antibacterial agents and food preservatives. Further studies are required to isolate and characterize the active compounds.