Antibacterial activities of oregano essential oils and their active components

Lei Tao ^1* Yan Liang ² Zhi Xia ² Xinsheng Wang ³ Xiaodong Wang ³ Zhe Chao ⁴ Jie Guo ¹

• ¹ Lanzhou Vocational Technical College, Lanzhou, China
• ² Henan Agricultural University, Zhengzhou, Henan Province, China
• ³ Oregano Technology Research Institute, Henan Shennong Authentic Medicinal Materials Co., Ltd,, Zhengzhou, China
• ⁴ Gansu Agricultural University, Lanzhou, Gansu Province, China

Oregano essential oils (OEOs) and their biological active components are of great interest due to their potent pharmaceutical and antibacterial activities. Herein, we investigated the antibacterial effects of OEOs extracted from wild and cultivated oregano with white or purple flower using our extraction process, as well as the in vitro antibacterial and synergistic effects of carvacrol and thymol, the main active components of OEOs. In in vitro antibacterial activity assays, essential oil extracted from wild and cultivated oregano with white flower exhibited potent antibacterial activities against standard strains of Gram-positive and -negative bacteria, with minimum inhibitory concentrations (MICs) range from 0.25-1 mg/mL. The antibacterial activities of carvacrol were obvious higher than that of thymol with MICs values of 0.005-0.04 mg/mL. These results were consistent with that against clinical isolates of MRSA. Furthermore, the synergism between carvacrol/thymol and seven common antibiotics against E.coli and MRSA was also detected using the checkerboard method. Carvacrol combining with tobramycin exhibited highly promising synergistic effects (with FICI = 0.25 against E.coli and 0.125 against MRSA), and their combined sensitivities against E.coli and MRSA were further confirmed by the time-kill assays.Preliminary explorations for synergistic mechanism suggested that the enhanced antibacterial potential of tobramycin might be attributed to carvacrol with the ability to perforate membrane and induce holes on it. Finally, a systemic infection mice model was established to evaluate the antibacterial activity of carvacrol combining with tobramycin. The results revealed that carvacrol combining with tobramycin exhibited potent in vivo antibacterial effects, with significantly improving the survival rate of mice, reducing the MRSA load and alleviating the pathological changes in the lungs of the infected mice.