Investigation of Chemical Composition, Antibacterial and Antioxidant Activity of Thymus daenensis and Thymus eriocalyx Essential Oils against Human Pathogenic Bacteria

Plant essential oils can be used as alternative agents for the treatment of antibiotic-resistant pathogenic bacteria. This study aimed to investigate the chemical composition, antibacterial, and antioxidant activity of Thymus eriocalyx and Thymus daenensis essential oils against Gram-positive and Gram-negative human pathogenic bacteria.

The aerial part of Thymus eriocalyx and Thymus daenensis in the full flowering stage were collected from West Azerbaijan Province (Urmia), Iran, in 2014. We obtained the essential oils using a Clevenger device. The disc diffusion method was used to determine the antibacterial activity of the essential oils against 15 Gram-positive and Gram-negative PTCC and ATCC bacterial standards. Minimum inhibitory concentrations (MICs) and minimum bactericidal concentrations (MBCs) were measured by microdilution broth method in 96-well plate and free radical scavenging activity by 2,2-diphenyl-1-picrylhydrazyl. Chemical analysis of the essential oils performed out by gas chromatography connected to Mass spectrometry.

Eleven (94.06%) and seven (90.76%) compounds were identified in T. eriocalyx and T. daenensis essential oils, respectively. The major components of T. eriocalyx essential oil were thymol (37.8%) and α-terpineol (14.91%), and of T. daenensis were thymol (52.36%) and carvacrol (16.72%). T. eriocalyx essential oil showed the highest activity against B. cereus with MIC of 0.93 μg mL- and MBC of 1.87 μg mL-. The most potent radical scavenging activity was also obtained for T. daenensis essential oil.

  Essential oil components of T. eriocalyx and T. daenensis may have the potential to be used as antimicrobial agents against antibiotic-resistant pathogenic bacteria.