Antibacterial Mechanism of Eugenol Against <i>Shigella sonnei</i> and Its Antibacterial Application in Lettuce Juice

Abstract

<i>Shigella sonnei</i> is a species of <i>Shigella</i>, and the infection rate of <i>S. sonnei</i> is increasing year by year. Eugenol is an active ingredient in clove essential oil and is a generally recognized as safe (GRAS)-certified food ingredient. The mechanism of inhibition of <i>S. sonnei</i> by eugenol has been investigated in this study. The minimum inhibitory concentration of eugenol against both <i>S. sonnei</i> ATCC 25931 and <i>S. sonnei</i> CMCC 51592 was 0.5 mg/mL and minimum bactericidal concentration (MBC) for both strains was 0.8 mg/mL. The inhibition effect of eugenol against <i>S. sonnei</i> was due to increased levels of reactive oxygen species in cells, changed cell membrane permeability, and induced cell membrane dysfunction, for instance, cell membrane hyperpolarization and intracellular ATP concentration drops. The results of confocal laser scanning microscope and field emission scanning electron microscopy showed that eugenol leads to decreased cell membrane integrity, resulting in changed cell morphology. Moreover, eugenol inactivated <i>S. sonnei</i> in Luria-Bertani (LB) broth and lettuce juice. These results indicated that eugenol could inactivate <i>S. sonnei</i> and has the potential to control <i>S. sonnei</i> in the food industry.