Study On The Growth Adaptation Mechanism Of Shiga Toxin-producing Escherichia Coli Under Different Stress Conditions

Shiga toxin-producing Escherichia coli(STEC)is an intestinal pathogen that causes zoonotic diseases by producing Shiga toxin.STEC can cause mild intestinal diseases such as watery diarrhea and hemorrhagic enteritis in humans,and can lead to hemolytic uremic syndrome and even death in severe cases.stx,one of the main virulence genes of STEC,encodes Shiga toxin(Stx),which has cytotoxicity,enterotoxicity and neurotoxicity.STEC usually enters the human body through food and water sources,leading to human infection and illness.Food processing is subject to a variety of pressures,including physical,chemical,and biological processing pressures.These pressures enable STEC to adapt to stress,improve its resistance to subsequent stress environments,and cause changes in its ability to produce toxins,which may bring greater safety risks to the food industry.Under the stress of food environment,STEC responds to the changes of living environment by adjusting the expression of related genes to enhance its adaptability to the uncomfortable environment.Therefore,it is necessary to explore the growth adaptation of STEC and its toxin production under the pressure of food processing environment,so as to provide data reference for the establishment of a safer processing environment in food processing industry,and to effectively prevent and control food safety incidents.In addition,to further explore the stress mechanism of growth adaptation of STEC under food stress and understand the gene expression profile under stress,so as to provide data support for the research of growth mechanism of STEC.In this study,the following work was performed:(1)The growth status and virulence of three STEC strains under different p H values(p H=5,7,and 9),salt concentrations(0.5%,1.5%,and 2.5% Na Cl),and growth pressures(10,25,and 37 ℃)were investigated.(2)Prokaryotic transcriptome sequencing was performed on STEC under p H=5,2.5% Na Cl and 10 ℃stress,and the gene expression of STEC under different stress pressures was analyzed.The main contents and results of this study are as follows:1.Growth status and virulence of STEC under different stressesThe growth curves of three STEC strains under different pH values,salt concentrations,temperature and pressure conditions were determined by colony counting method.The production ability of STEC strains under different pressure conditions was determined by cytotoxicity test.The results showed that the growth and virulence of STEC under different stress conditions were significantly different,and different gradients of each stress condition also had different effects.Under different p H pressures,the growth of STEC was more inhibited under acidic pressure than under alkaline pressure,and the production ability of STEC was weaker than that under neutral condition in the control group,while the production ability of STEC under alkaline condition was higher than that in the control group.Under different salt concentrations,except for strain D3146,with the increase of salt concentration,the growth inhibition and cell damage of STEC were enhanced.Under different temperature pressures,the growth inhibition of STEC increased with the decrease of temperature,mainly reflected in the decrease of μmax value and the increase of λ value.However,the growth of STEC was continuously increased during the inhibition process.Compared with the control group,the maximum concentration of STEC was greatly increased,and the toxic effect on cells was also increased.2.Stress mechanisms of STEC under different stress conditionsProkaryotic transcriptome sequencing was performed on STEC under p H=5,2.5%Na Cl and 10 ℃ growth stress,and the gene expression of STEC was analyzed.The results showed that the differentially expressed genes of STEC under different stress conditions were different,and the stress mechanisms dominated by genes were different.The results of transcriptome sequencing showed that 975,960 and 1785 differentially expressed genes were detected in STEC under acid,high salt and low temperature stress,respectively.GO enrichment and annotation results showed that the three different pressures had the greatest impact on the ribosomal structural components and functionally related genes such as ribonucleoprotein and translation of STEC.KEGG annotation results showed that acid pressure and low temperature pressure had the greatest impact on carbohydrate metabolism and membrane transport pathways of STEC,while high salt pressure had the greatest impact on energy metabolism and membrane transport pathways of STEC.In addition,Ipath pathway analysis showed that the change of STEC virulence under pressure may be related to the expression of flagellar component related genes.