In Vitro Antibacterial Activity of Aqueous Extracts from Selected Palestinian Wild Medicinal Plants Against Escherichia coli and Staphylococcus aureus

Abstract

Background: Medicinal plants are widely used in traditional medicine and may represent a potential source of natural antimicrobial compounds. This study evaluated the antibacterial activity of aqueous extracts from five medicinal plants: Paronychia argentea, Plantago major, Ocimum basilicum, Laurus nobilis, and Artemisia absinthium, against Gram-positive and Gram-negative bacterial strains. Methods: Plant materials were dried and extracted by maceration in distilled water, and crude aqueous extracts were prepared at different concentrations. Antibacterial activity was assessed against Staphylococcus aureus (S. aureus, ATCC 29737) and Escherichia coli (E. coli, ATCC 8739) using agar well diffusion and minimum inhibitory concentration (MIC) assays. All experiments were performed in triplicate with appropriate solvent and antibiotic controls. Results: The aqueous plant extracts demonstrated selective antibacterial activity against S. aureus, with inhibition zones ranging from 14 to 21 mm. Paronychia argentea produced the largest inhibition zone (21 mm). However, after normalization for extract mass, Artemisia absinthium and Ocimum basilicum exhibited greater antibacterial activity per milligram, suggesting higher intrinsic potency. These findings were consistent with the MIC results, in which O. basilicum and A. absinthium showed the lowest MIC values (0.4 mg/mL), followed by P. major and L. nobilis (0.8 mg/mL), whereas P. argentea had a MIC of 2 mg/mL. No inhibition zones were observed against E. coli in the agar diffusion assay, although minor inhibitory effects were detected by broth microdilution at higher extract concentrations. Conclusion: The findings indicate that some Palestinian medicinal plants contain water-soluble compounds with antibacterial activity, particularly against the Gram-positive bacterium S. aureus. Ocimum basilicum and Artemisia absinthium demonstrated the greatest antibacterial potency based on MIC and mass-normalized activity. These preliminary findings provide baseline evidence supporting further phytochemical and mechanistic investigations to identify the active compounds and characterize their antibacterial effects.