Evaluation of Antimicrobial Activity of Cymbopogon citratus Essential Oil Alone and in Combination with Origanum majorana and Caryophyllus aromaticus Essential Oils against Some Foodborne Bacteria

Background: Food spoilage and foodborne diseases are two important problems in the food industry. On the other hand, consumers’ tendency to use natural additives is increasing. Hence, plant essential oils (EOs) can be safe alternatives in this regard. Objective: The objectives were to determine the chemical composition and to evaluate the antimicrobial activity of Cymbopogon citratus EO against some foodborne bacteria alone and in combination with Origanum majorana and Caryophyllus aromaticus EOs. Materials and Methods: Chemical composition of C. citratus EO was analyzed by gas chromatography-mass spectrometry. Further, antibacterial activity of the EO against foodborne bacteria was assessed using disk diffusion method. In addition, the minimum inhibitory concentration of the EO was determined by microdilution broth method and then the minimum bactericidal concentration value was determined. Checkerboard synergy testing was also performed to determine the fractional inhibitory concentration index. Finally, time-kill curves were drawn based on the bacterial population (CFU/mL) against time (h). Results: The major compounds of C. citratus EO were isothymol, thymol, trans-caryophyllene, and cymene. The most and the least sensitive foodborne bacteria to C. citratus EO were Staphylococcus aureus and Bacillus subtilis, respectively. The minimum inhibitory concentration (MIC) values of C. citratus EO against all the evaluated bacteria were 0.1% and The minimum bactericidal concentration (MBC) values ranged between 0.1 and >2% (v/v). The combination of C. citratus and O. majorana EOs showed a synergistic activity against Salmonella typhimurium and partial synergism against B. subtilis, Escherichia coli O157:H7, S. aureus, and Listeria monocytogenes. Moreover, the combination of C. citratus and C. aromaticus EOs demonstrated partial synergism against S. aureus and L. monocytogenes, and additive interaction against S. typhimurium; however, the combination was indifferent against E. coli O157:H7 and B. subtilis. Furthermore, C. citratus plus O. majorana EOs and C. citratus plus C. aromaticus EOs showed a bactericidal effect against S. typhimurium after 24 hours in the time-kill assay. Conclusion: In general, the synergism, partial synergism, and additive effects of C. citratus in combination with C. aromaticus and O. majorana EOs strengthen the antimicrobial activity, expand the spectrum of activity, reduce the concentrations required, decrease the side effects, and prevent the alteration of organoleptic properties of food.