Chemical composition and antibacterial properties of Ocimum basilicum, Salvia officinalis and Trachyspermum ammi essential oils alone and in combination with nisin

Background and objectives: Plant essential oils are sometimes considered for use as antimicrobial agents in foods and medicines and they could be combined with other antimicrobial agents to strengthen the effect and/or reduce the required dose. This study was conducted to determine the chemical composition of the Ocimum basilicum, Salvia officinalis and Trachyspermum ammi essential oils and evaluate their antibacterial efficiency, alone and in combination with nisin, against Escherichia coli O 157 and Staphylococcus aureus. Methods: The chemical composition of three essential oils (Ocimum basilicum, Salvia officinalis and Trachyspermum ammi) were determined by gas chromatography/mass spectrometry. Further, their antibacterial properties and the synergistic effect of the combination of three essential oils and nisin were also assessed against Escherichia coli and Staphylococcus aureus. The antibacterial activity was determined by evaluation of minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) by broth dilution method in 96-well microplates. The synergistic effects were tested by the checkerboard method and the fractional inhibitory concentration (FIC) index was calculated. Results: The major components of O. basilicum, S. officinalis and T. ammi were linalool (35.99%), 1,8-cineole (22.91%) and p-Cymene (35.5%), respectively. In general, all of the essential oils as well as nisin exerted more considerable antibacterial effects against Gram-positive bacteria than Gram-negative one. The essential oil of T. ammi showed the highest activity against S. aureus with MIC (≤0.078 mg/mL) and MBC (≤0.156 mg/mL). The combined application showed synergistic activity against E. coli but no change in activity was observed against S. aureus. The most synergistic effect was observed for the combination of nisin and S. officinalis (FIC 0.03). Conclusion: It can be concluded that nisin could enhance the antibacterial potential of the essential oils.