Phenethyl Isothiocyanate Inhibits Shiga Toxin Production in Enterohemorrhagic Escherichia coli by Stringent Response Induction

Abstract

bThe pathogenicity of enterohemorrhagic Escherichia coli (EHEC) depends on production of Shiga toxins, which are encoded by stx genes located in the genomes of lambdoid prophages. Efficient expression of these genes requires prophage induction and lytic development of phages. Treatment of EHEC infections is problematic due to not only the resistance of various strains to antibiotics but also the fact that many antibiotics cause prophage induction, thus resulting in high-level expression of stx genes. Here we report that E. coli growth, Shiga toxin-converting phage development, and production of the toxin by EHEC are strongly inhibited by phenethyl isothiocyanate (PEITC). We demonstrate that PEITC induces the stringent response in E. coli that is mediated by massive production of a global regulator, guanosine tetraphosphate (ppGpp). The stringent response induction arises most probably from interactions of PEITC with amino acids and from amino acid deprivation-mediated activation of ppGpp synthesis. In mutants unable to synthesize ppGpp, development of Shiga toxin-converting phages and production of Shiga toxin are significantly enhanced. Therefore, ppGpp, which appears at high levels in bacterial cells after stimulation of its production by PEITC, is a negative regulator of EHEC virulence and at the same time efficiently inhibits bacterial growth. This is in contrast to stimulation of virulence of different bacteria by this nucleotide reported previously by others.

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

“…In this study, not only did the abundance of the Stx2-converting phage decrease, the total number of phage decreased proportionally with the increase of cinnamon oil concentration, which explained the reduction of Stx2 production. A similar phenomenon was observed in that subinhibitory concentrations of phenethyl isothiocyanate, which is a derivative of glucosinolate found in cruciferous vegetables, significantly reduced the amount of Stx-encoding phage and stx expression in E. coli O157:H7 (58).…”

The antibacterial properties of isothiocyanates

“…Indeed, supplementation of glycine or arginine in the growth medium, thereby increasing the pool of free amino acids at inhibitory concentrations of ITC, was able to restore growth of bacterial cultures treated with PEITC and increased the MIC of PEITC for E. coli. This MIC-increasing effect was also observed by supplementing lysine, methionine, phenylalanine, serine and threonine (Nowicki et al, 2014). The antibacterial properties of isothiocyanates…”

“…Induction of a stringent response Nowicki et al (2014) have reported the efficacy of PEITC in inhibiting the growth of enterohaemorrhagic E. coli (EHEC) as well as Shiga toxin production. The authors correlated these effects to the induction of a stringent response.…”

Shiga toxins and stx phages: highly diverse entities

“…Such factors include hydrogen peroxide (Wagner et al, 2001;Łoś et al, 2009, 2010, high temperature in combination with UV irradiation (Yue et al, 2012), EDTA (Imamovic & Muniesa, 2012), sodium citrate (Imamovic & Muniesa, 2012;Nejman-Faleń czyk et al, 2012), amino acid starvation (Nejman-Faleń czyk et al, 2012), phenethyl isothiocyanate (Nowicki et al, 2014), DNase colicins (Toshima et al, 2007), high hydrostatic pressure (Aertsen et al, 2005a), sodium chloride (Łoś et al, 2009;Harris et al, 2012), nitric oxide (Vareille et al, 2007), 60 Co irradiation (Yamamoto et al, 2003) Łoś et al, 2009;Nassar et al, 2013), as well as those antibacterials used as growth promoters in animal production (Köhler et al, 2000).…”