Cinnamon Oil Inhibits Shiga Toxin Type 2 Phage Induction and Shiga Toxin Type 2 Production in Escherichia coli O157:H7

Abstract

This study evaluated the inhibitory effect of cinnamon oil against Escherichia coli O157:H7 Shiga toxin (Stx) production and further explored the underlying mechanisms. The MIC and minimum bactericidal concentration (MBC) of cinnamon oil against E. coli O157:H7 were 0.025% and 0.05% (vol/vol), respectively. Cinnamon oil significantly reduced Stx2 production and the stx 2 mRNA expression that is associated with diminished Vero cell cytotoxicity. Consistently, induction of the Stx-converting phage where the stx 2 gene is located, along with the total number of phages, decreased proportionally to cinnamon oil concentration. In line with decreased Stx2 phage induction, cinnamon oil at 0.75؋ and 1.0؋ MIC eliminated RecA, a key mediator of SOS response, polynucleotide phosphorylase (PNPase), and poly(A) polymerase (PAP I), which positively regulate Stx-converting phages, contributing to reduced Stx-converting phage induction and Stx production. Furthermore, cinnamon oil at 0.75؋ and 1.0؋ MIC strongly inhibited the qseBC and luxS expression associated with decreased AI-2 production, a universal quorum sensing signaling molecule. However, the expression of oxidative stress response genes oxyR, soxR, and rpoS was increased in response to cinnamon oil at 0.25؋ or 0.5؋ MIC, which may contribute to stunted bacterial growth and reduced Stx2 phage induction and Stx2 production due to the inhibitory effect of OxyR on prophage activation. Collectively, cinnamon oil inhibits Stx2 production and Stx2 phage induction in E. coli O157:H7 in multiple ways. IMPORTANCEThis study reports the inhibitory effect of cinnamon oil on Shiga toxin 2 phage induction and Shiga toxin 2 production. Subinhibitory concentrations (concentrations below the MIC) of cinnamon oil reduced Stx2 production, stx 2 mRNA expression, and cytotoxicity on Vero cells. Subinhibitory concentrations of cinnamon oil also dramatically reduced both the Stx2 phage and total phage induction in E. coli O157:H7, which may be due to the suppression of RNA polyadenylation enzyme PNPase at 0.25؋ to 1.0؋ MIC and the downregulation of bacterial SOS response key regulator RecA and RNA polyadenylation enzyme PAP I at 0.75؋ or 1.0؋ MIC. Cinnamon oil at higher levels (0.75؋ and 1.0؋ MIC) eliminated quorum sensing and oxidative stress. Therefore, cinnamon oil has potential applications as a therapeutic to control E. coli O157:H7 infection through inhibition of bacterial growth and virulence factors. E scherichia coli O157:H7 is an important foodborne pathogen that is associated with hemorrhagic colitis, hemolytic-uremic syndrome (HUS), and death (1). More than 63,000 cases of foodborne illness are estimated to be caused by E. coli O157:H7 annually in the United States (2). Outbreaks have been associated with ground beef, ready-to-eat salad, cheese, apple juice, and other foods (3-6).Shiga toxin (Stx) is a major virulence factor of E. coli O157:H7. Its production in the gastrointestinal tract in conjunction with other virulence factors induces hemorrhagic colitis, and its entry...

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