The Antibacterial Activity of Selected Labiatae (Lamiaceae) Essential Oils against Brucella melitensis

Background: Brucellosis, a zoonosis caused by four species of brucella, has a high morbidity. The major cause of brucellosis worldwide is brucella melitensis. Medicinal plants are considered as new antibacterial sources that could replace conventional antibiotics in the treatment of antibiotic-resistant bacteria. The aim of this study was to evaluate the efficacy of some native plants, alone and in combination with some antibiotics, in the treatment of brucellosis. Methods: The present experimental in vitro study was carried out to evaluate the anti-brucella activities of essential oils of Rosmarinus officinalis L., Origanum syriacum, Thymus syriacus, Salvia palaestina Benth, Mentha piperia, and Lavandula stoechas L., alone and in combination with some antibiotics. The activity against 16 tetracycline-resistant B. melitensis isolates was determined by disc diffusion method incorporating a concentration of 5%. Antibiotic discs were also used as a control. Microdilution brucella broth susceptibility assay was used in order to determine the MICs of essential oils and five antibiotics. Results: Among all the herbs evaluated, only the essential oils of O. syriacum and T. syriacus plants demonstrated most effective anti-brucella activity, and were then chosen for MIC study. The minimal inhibitory concentrations (MIC(50)) of essential oils of O. syriacum and T. syriacus against tetracycline-resistant B. melitensis were 3.125 µl/ml and 6.25 µl/ml, respectively. Conclusion: Among the essential oils studied, those of O. syriacum and T. syriacus were most effective. Since a combination of levofloxacin and Thymus syriacus essential oil increased the efficacy of this antibiotic, O. syriacum and T. syriacus are recommended to be used as bactericidal agents against B. melitensis.