Antimicrobial mechanism of the major active essential oil compounds and their structure–activity relationship

Plant essential oils possess many sorts of bioactivities including microbicidal property. A number of essential oil components have been characterized as effective antibacterial agents. In this study, we selected several major antibacterial essential oil compounds and investigated their inhibition against 1-deoxy-D-xylulose 5-phosphate reductoisomerase, the key enzyme of the 2-methyl-D-erythritol 4-phosphate terpenoid biosynthetic pathway and also a validated target for screening novel antibiotics. The results show that compounds eugenol and carvacrol display medium to weak inhibition against 1-deoxy-D-xylulose 5-phosphate reductoisomerase with IC50 values being about 97.3 and 139.2 μM, repectively; Compounds thymol, geraniol, linalool, and nerol exhibit weak 1-deoxy-D-xylulose 5-phosphate reductoisomerase inhibitory activity while perillaldehyde, cinnamaldehyde, α-terpineol, and citral possess undetectable inhibition against1-deoxy-D-xylulose 5-phosphate reductoisomerase. Based on these data, the structure–activity relationship of these compounds is discussed. Additionally, the inhibition kinetics of carvacrol and eugenol are also determinated. These results can not only deepen our understanding toward the antimicrobial mechanisms of eugenol and carvacrol, but also direct the reasonable application of these antimicrobial agents in medical pathology and in the control of plant diseases as well as in food industry.