Background and Aim: Enterohemorrhagic Escherichia coli O157:H7 (EHEC) causes foodborne outbreaks worldwide and the bacteria form antimicrobial-tolerant biofilm. We investigated the abilities of Thymus daenensis and Satureja hortensis essential oils (EOs) to inhibit bacterial growth, biofilm formation and quorum sensing (QS) by E. coli O157:H7. Methods: The tested EOs were isolated from plant material by hydrodistillation and analyzed under chromatography-mass spectrometry. The antibacterial and anti-biofilm activities of the EOs were determined by microdilution broth and microtiter-plate (MtP) tests, respectively. The QS inhibitory (QSI) potential was examined by inhibition of swimming and swarming motility at sub-MIC levels. Real-time quantitative reverse transcription PCR (RT-qPCR) was used to determine the expression of QS-system-related genes. Results: The MICs for T. daenensis and S. hortensis EOs against EHEC were 3.12 and 6.25 μg/mL, respectively and the MBCs were 6.25 and 12.5 μg/mL, respectively. The MtP test showed a significant (p < 0.05) inhibitory and disruptive effect on both EOs for EHEC biofilm formation at MIC/2 (1.56 μg/mL for T. daenensis; 3.12 μg/mL for S. hortensis) and MIC/4 (0.78 μg/mL for T. daenensis; 1.56 μg/mL for S. hortensis) concentrations. Gene expression analysis revealed significant down-regulation of luxS and pfs following treatment with MIC/2 concentrations. Conclusion: The results of the present research point to the promising antibacterial, anti-biofilm and anti-QS potential of T. daenensis and S. hortensis EOs against E. coli O157:H7.
