Evaluation of the Antimicrobial Activity of 20 Essential Oils and Their Combinations on Bacterial and Fungal Strains

Growing antibiotic resistance is driving the search for natural alternatives, such as essential oils (EOs), which are known for their antimicrobial properties. This study evaluated the antimicrobial efficacy of 20 EOs on bacterial and fungal strains and the impact of their combinations.

Twenty EOs were selected to evaluate their antimicrobial potential in vitro. Stock solutions were prepared and tested on three bacterial strains (Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa) and three yeast strains of the genus Candida. The antimicrobial activity of EOs was initially evaluated by aromatogram, making it possible to classify oils according to their effectiveness. The sensitivity of microorganisms to EOs was then determined by measuring the minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC). EO combination tests were also performed to detect synergistic or antagonistic effects.

Tests revealed that Origanum vulgare, Cymbopogon citratus, and Thymus leptobotrys were particularly effective against Gram-positive bacteria and yeasts, while others, such as Citrus limon, showed negligible activity. The combinations of oils generally produced indifferent or antagonistic effects, especially against P. aeruginosa. Conclusion: The results could open new perspectives for natural antimicrobial treatments, thus contributing to the fight against antibiotic resistance. In addition, the study will highlight the importance of judicious use of EO combinations to avoid interactions that could compromise their effectiveness.