Investigation the antimicrobial activities and mechanisms of action of essential oils against Campylobacter spp.

In this study, cardamom, cumin, dill weed, thyme, oregano, fennel, ginger and basil essential oils were evaluated for their antibacterial activities against Campylobacter jejuni and Campylobacter coli. Additionally, essential oils were tested for their chemical compositions by gas chromatography and gas chromatography-mass spectrometry. Initial screening of antimicrobial activity of the essential oils was studied using an agar-well diffusion assay by measuring the diameter of the inhibition zone. Minimum inhibition concentration and minimum bacteriocide concentration values were determined by broth microdilution and agar dilution methods for standard and clinical isolates of Campylobacter spp. respectively. Using agar-well diffusion assay, all EOs inhibited the growth of tested bacteria at variable levels. The maximum diameter of inhibition zone and minimum MIC values were obtained for cardamom, cumin, dill weed, oregano, and thyme essential oils. Essential oils were also analysed for their diffusion abilities. Essential oils with low antimicrobial activities also have low diffusion coefficients and high oil droplet sizes. Relative electrical conductivity, release of cell constituents and extracellular ATP concentrations were determined in order to determine the mechanism of antimicrobial action. The results showed that after exposure to esssential oils, relative electrical conductivity, release of cell constituents and extracellular ATP concentrations increased significantly with the increased concentration of the essential oil. These results indicated that tested essentail oils caused disruption of the cytoplasmic membrane which became increasingly permeable and loss of their integrity and might be responsible for the antibacterial activity, led to the losses of cell constituents and cell death.