Comprehensive Evaluation of the Antibacterial Activity of Teucrium brevifolium from the Libyan Coastal Region

Abstract

The emergence of multidrug-resistant (MDR) bacteria represents one of the most serious global health challenges, necessitating the search for new antibacterial agents from natural sources. Teucrium brevifolium Schreb., locally known in Libya as Al-Juraydah, is an under-investigated Libyan medicinal plant; however, studies on its antibacterial activity remain limited. This study aimed to evaluate the antibacterial activity of the ethyl acetate extract of T. brevifolium collected from the Libyan coastal region against a panel of clinically important bacterial strains, including a clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA), and to investigate its synergistic effects with conventional antibiotics. An ethyl acetate extract was prepared from the aerial parts of the plant through ethanol extraction followed by solvent fractionation. Antibacterial activity was evaluated using disc diffusion, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) assays. Synergistic interactions with conventional antibiotics were assessed using the checkerboard method and the fractional inhibitory concentration index (FICI). Preliminary phytochemical screening was also performed using standard qualitative protocols. The ethyl acetate extract exhibited weak to moderate broad-spectrum antibacterial activity. MIC values of 8, 8, 16, 16, 16, 32, and 32 mg/mL were recorded against S. aureus, Bacillus subtilis, MRSA, Salmonella Typhi, Escherichia coli, Klebsiella pneumoniae, and Pseudomonas aeruginosa, respectively. The MBC/MIC ratio was 2.0 for all tested strains, indicating a bactericidal effect. Synergistic interactions were observed with several antibiotics, with a strong interaction between the extract and oxacillin against the MRSA clinical isolate (FICI = 0.375). Preliminary phytochemical screening revealed the presence of flavonoids, phenolics, and terpenoids. The ethyl acetate extract of Libyan T. brevifolium exhibited weak to moderate broad-spectrum antibacterial activity with bactericidal properties and showed synergistic interactions with selected conventional antibiotics, including against MRSA. However, the relatively high MIC values limit the immediate therapeutic applicability of the crude extract. Advanced phytochemical investigation is recommended to identify the active constituents. These findings support further studies, including animal-model investigations and isolation of bioactive compounds.