Evaluating the effect of Nanoemulsion of Artemisia dracunculus Essential Oil on Expression of virulence genes in enterohemorrhagic Escherichia coli

​Escherichia coli O157:H7 is one of the most important and common foodborne pathogens in the world which is being resistant against some current synthetic antimicrobials. The aim of this study was to determine the minimum inhibitory concentration (MIC) and the minimum bacterial concentration (MBC) of Artemisia dracunculus (tarragon) essential oil and its nanoemulsion for enterohemorrhagic strain of Escherichia coli and then the effect of sub-MIC concentrations on growth rate and gene expression of virulence genes (stx1A and stx2A). Nanoemulsion of tarragon essential oil was prepared by the ultrasound method and the droplet size and zeta potential were determined. MIC and MBC of essential oil and nanoemulsion were determined using the broth microdilution method. The growth rate and expression of stx1A and stx2A genes in Escherichia coli were assessed after treatment with different concentrations of sub-MICs of essential oil and nanoemulsion. Estragol was identified as the main component in the essential oil. The average diameter of nanoemulsion particle was 50 nm and the zeta potential was -30mV. The MIC values ​​ of essential oil and nanoemulsion were 0.58±0.11 and 0.33±0.07mg/ml, respectively, and their MBC were 0.65 ± 0.20 and 0.38 ± 0.15 mg/ml, respectively. Nanoamulsion had a greater inhibitory effect against bacterial growth than free essential oil. At the end of the 72-hour period, nanoemulsion treatment at 75% MIC resulted in a reduction in stx1A and stx2A transcription of 3.75 and 4.10 folds, while at 75% MIC of essential oil stx1A and stx2A transcripts were reduced 1.91 and 2.02 folds compared with control, respectively. Higher activity of nanoemulsion of tarragon essential oil to reduce the growth and shigatoxin production of E. coli compared to pure EO, reveals its potential to be used as a natural food preservative and a solution to the global problem of emergence of antibiotic-resistant microbes.