Chemical Composition and Antibacterial Activity of Artemisia herba-alba Essential Oil from Libya Against Multidrug-Resistant Pseudomonas aeruginosa and Methicillin-Resistant Staphylococcus aureus

Abstract

Antimicrobial resistance, particularly multidrug resistance (MDR), represents a major global concern, and there has been increased interest in natural products as potential sources of alternative antimicrobial agents. Artemisia herba-alba is an aromatic medicinal plant traditionally used in Libya. This study aimed to extract the essential oil from A. herba-alba collected in the Al-Abraq region of northeastern Libya, characterise its chemical composition, and evaluate its antibacterial activity against selected clinical isolates, including MDR Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA). Essential oil was obtained from dried aerial parts by hydrodistillation using a Clevenger-type apparatus and characterised by gas chromatography-mass spectrometry (GC-MS). Antibacterial activity was evaluated using disc diffusion and broth microdilution assays to determine minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC), characterised by antimicrobial susceptibility testing according to CLSI recommendations. Statistical comparisons were performed using the Mann-Whitney U test, with p ≤ 0.05 considered significant. The essential oil yield was 2.0% (w/w). GC-MS analysis identified 40 compounds representing 97.21% of the total oil composition. Camphor (30.76%) and 1,8-cineole (16.96%) were the predominant constituents, followed by camphene (6.85%), chrysanthenone (5.56%), and borneol (4.89%). The essential oil showed concentration-dependent antibacterial activity. MIC values ranged from 0.78 to 6.25 μL/mL (v/v), whereas MBC values ranged from 1.56 to 12.50 μL/mL (v/v). Clinical resistant isolates generally showed lower susceptibility than corresponding reference strains. The MBC/MIC ratio was consistently 2 across all tested groups, supporting a bactericidal effect under the experimental conditions. The essential oil of Libyan A. herba-alba demonstrated promising in vitro antibacterial activity against reference strains and clinically resistant isolates. Further studies involving larger numbers of isolates, cytotoxicity assessment, mechanistic investigations, and in vivo models are required.