Synergistic antibacterial activity of the essential oils from three medicinal plants against some important food-borne pathogens by microdilution method

Essential oils of three medicinal plants species, including Carum copticum (L.) C. B. Clarke, Bunium persicum (Boiss.) B. Fedtsch. and Cuminum cyminum L., were obtained by hydrodistillation and their constituents were analyzed by GC and GC/MS using retention indices and fragmentation patterns. The antibacterial effects (MIC and MBC) of the essential oils were assessed on several food-borne pathogens, namely Staphylococcus aureus, Bacillus cereus, Escherichia coli O157: H7, Salmonella enteritidis and Listeria monocytogenes by microdilution technique using ELISA reader. Because of the combinatory usage of Bunium persicum and Cuminum cyminum in folk medicine, the affect of essential oil on food organoleptic properties and MIC values of the plants, interaction of Bunium persicum and Cuminum cyminum essential oils were also studied by FICindex determination using modified dilution checkboard method. The results showed that there are noticeable differences between the essential oils as their constituents as concerned, while ρ-cymen and γ-terpinene detected in all essential oils in different percentage. The main components of essential oils of C. copticum were thymol (48.4%), ρ-cymene (21.8%) and γ-terpinene (21.3%). The major constituents of B. persicum were γ-terpinene (44.2%), cuminaldehyde (16.9%), γ-terpinen-7-al (10.5%), and ρ-cymen (8%) while those of C. cyminum were cuminaldehyde (30.2%), ρ-cymene (14.1%), γ-terpinene (12.8%), and safranal (9.4%). The ranges of minimum inhibitory concentration of the oils were 0.03-0.5, 0.18-3.0, and 0.37-3.0 mg/ml, respectively, for C. copticum, B. persicum and C. cyminum. Moreover, the combination of B. persicum and C. cyminum essential oils confirmed synergistic and additive activities against the pathogens. In conclusion, although the MIC of Bunium persicum and Cuminum cyminum essential oils were lower than C. copticum, but combinatory usage of these essential oils especially against gram-positive bacteria produced promissing results. So application of these essential oils is recommended in combination as an efficients and complementary method for control of food borne pathogens with lower side effects on organolpetic properties of food.