In this study, the antimicrobial mechanism of cinnamaldehyde (CIN) against Gram-negative Escherichia coli ATCC 25922 (E. coli) based on membrane and gene regulation was investigated. Treatment with low concentration (0, 1/8, 1/4, 3/8 MIC) of CIN can effectively suppress the growth of E. coli by prolonging its lag phase and Raman spectroscopy showed obvious distinction of the E. coli after being treated with these concentration of CIN. The determination of relative conductivity indicated that CIN at relatively high concentration (0, 1, 2, 4 MIC) can increase the cell membrane permeability, causing the leakage of cellular content. Besides, the content of malondialdehyde (MDA) and the activity of total superoxide dismutase (SOD) of E. coli increased with increasing treatment concentration of CIN, implying that CIN can cause oxidative damage on E. coli cell membrane and induce the increase of total SOD activity to resist this oxidative harm. Moreover, quantitative real-time RT-PCR (qRT-PCR) analysis revealed the relationship between expression of antioxidant genes (SODa, SODb, SODc) and treatment CIN concentration, suggesting that SOD, especially SODc, played a significant role in resistance of E. coli to CIN. The underlying inactivation processing of CIN on E. coli was explored to support CIN as a potential and natural antimicrobial agent in food industry.
Keywords: Cinnamaldehyde; Escherichia coli; Gene regulation; Membrane permeability; Oxidation.