A Comparative Evaluation of Agar Diffusion and Volatilization Methods For Assessing the Antibacterial Activity of essential oil of Libyan Artemisia judaica Against Pathogenic Bacteria

Abstract

Background: Antimicrobial resistance (AMR) poses a serious global health challenge, demanding alternative therapeutic options. Essential oils (EOs) are complex, volatile mixtures with broad-spectrum antimicrobial properties and reduced likelihood of resistance development. Artemisia judaica has been traditionally used for its medicinal effects, yet limited data exist regarding its antibacterial potential against clinically relevant pathogens under different assay conditions.

Objectives: This study aimed to evaluate and compare the antibacterial activity of A. judaica essential oil against Staphylococcus aureus and Pseudomonas aeruginosa using agar diffusion (direct contact) and volatilization (vapour phase) assays.

Methods: Aerial parts of A. judaica collected from Al-Awaynat (Libya) were subjected to hydrodistillation via a Clevenger-type apparatus to obtain the EO. Antibacterial activity was assessed against S. aureus and P. aeruginosa following CLSI-adapted protocols. Agar well diffusion and volatilization assays were employed, with levofloxacin serving as a positive control. Zones of inhibition (ZOIs) were measured, and mean values ± standard deviation were recorded.

Results: The EO yield was 0.8% ± 0.05 (v/w). In agar diffusion assays, inhibition zones measured 13.5 ± 2.1 mm for S. aureus and 24.3 ± 5.6 mm for P. aeruginosa, with activity against P. aeruginosa surpassing levofloxacin (20.5 ± 0.7 mm). By contrast, volatilization assays showed minimal and uniform activity (8.0 ± 0.0 mm) for both strains, indicating limited vapour-phase antibacterial potential.

Conclusion: A. judaica essential oil demonstrates strong antibacterial activity in direct-contact assays, particularly against P. aeruginosa, but negligible vapour-phase effects. These findings suggest its potential application in topical or direct-contact formulations rather than airborne disinfection, and highlight the importance of assay selection in EO bioactivity profiling.