Purpose: This study tested the inhibitory effect of cinnamon oil against E. coli O157:H7, and for the first time, evaluated its influence on Stx2 production, Vero cell cytotoxicity, and Stx2 phage induction.
Methods: Antimicrobial activity was measured by disc diffusion assay, minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), and death curve. Western blotting, real-time quantitative RT-PCR and in vitro Vero cell culture were used to analyze Stx2 production, stx2 mRNA expression and cytotoxicity, respectively. Stx phage induction was measured by plaque forming units coupled with real time quantitative PCR.
Results: MIC and MBC were 0.025% and 0.05% (v/v), respectively; two times of MBC showed bactericidal effect within 15 min, while three fold of MBC resulted in a 6-log reduction during 30 min incubation. Sub-inhibitory concentrations of cinnamon oil decreased Stx2 production, stx2 mRNA expression, and cytotoxicity in a dose dependent manner (P < 0.05); ¾ or 1 MIC reduced Stx2 production and stx2 mRNA expression to undetectable level. Consistently, the phage titer and Stx2 phage DNA decreased proportionally to cinnamon oil concentrations, and beyond the detection level when cinnamon oil concentration increased to ¾ and 1 MIC.
Significance: Cinnamon oil has the potential to be used as a promising natural compound to control E. coli O157:H7 and Stx production.