Cinnamon Oil Inhibits Shiga Toxin Type 2 Phage Induction and Shiga Toxin Type 2 Production in Escherichia coli O157:H7
ABSTRACTThis study evaluated the inhibitory effect of cinnamon oil againstEscherichia coliO157:H7 Shiga toxin (Stx) production and further explored the underlying mechanisms. The MIC and minimum bactericidal concentration (MBC) of cinnamon oil againstE. coliO157:H7 were 0.025% and 0.05% (vol/vol), respectively. Cinnamon oil significantly reduced Stx2 production and thestx2mRNA expression that is associated with diminished Vero cell cytotoxicity. Consistently, induction of the Stx-converting phage where thestx2gene 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 theqseBCandluxSexpression associated with decreased AI-2 production, a universal quorum sensing signaling molecule. However, the expression of oxidative stress response genesoxyR,soxR, andrpoSwas 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 inE. coliO157: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,stx2mRNA expression, and cytotoxicity on Vero cells. Subinhibitory concentrations of cinnamon oil also dramatically reduced both the Stx2 phage and total phage induction inE. coliO157: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 controlE. coliO157:H7 infection through inhibition of bacterial growth and virulence factors.