Survival Of Escherichia Coli O157:H7 In The Soils Under Freeze-thaw Cycling Conditions

The freeze-thaw cycle is a common natural phenomenon in seasonal frozen land zones in northern China,mostly in early spring or late autumn.The freeze-thaw cycle affects soil physical and chemical properties,which in turn influences the survival of microorganisms in soil.E.coli O157:H7 is a pathogen largelyoriginatedfrom the feces of livestock and poultry.It mainly transmits via fecal to mouth and may cause hemorrhagic diarrhea and enteritis after infection.Secondary hemolytic uremic syndrome,thrombotic thrombocytopenic purpura and other diseases may result in death.Therefore,understanding of the survival behavior of E.coli O157:H7 in the soil environment and identification of thefactors affecting its survival are of greatimportancein prevention and treatment ofE.coli O157:H7 infection.This study was simulated in the laboratory under three different freeze-thaw cycles(-6?/+6??-10?/+6??-14?/+6?),In this study,the survival behavior of E.coli O157:H7 in 12 soil samples from three apple-pear farms(YJ,LJ,HL)in Yanbian Korean Autonomous Prefecture was simulated.The freeze-thaw cycle is very common in this area.The Weibull model was used to simulate the survival dynamics of E.coli O157:H7,and the time to reach the minimum detection limit(ttd)was calculated.Multivariate stepwise regression analysis was used to identify the key factors affecting the survival of E.coli O157:H7.At the same time,the microbial community composition in the soil before E.coli O157:H7 inoculation was investigated,and the characteristics of the composition and structure of bacteria and fungi communities in the soil and theirrelationship with survival parameters were explored.Experimental results were showed as below:(1)Principal Co-ordinates Analysis(PCoA)results showed that the species and community number of bacterial fungi in soil from three different apple-pear farmsare different.Among them,the most abundant bacterial phylais Actinobacteria.The most abundant gat fungi phylais Ascomycota.Thesequencing result is in line with the general trendof microbial community composition in soils in northern China.(2)The results of survival experiments showed that the number of E.coli O157:H7 decreased with the increase of incubationtime under different freezing-thawing setup,and showed a concave survival curve(p<1),indicating that the number of bacteria deceasedfast initiallyand tended to deceaseslowly afterword.Compared with the control group,the number of E.coli O157:H7 bacteria undergoing freeze-thaw cycles decreased significantly,showingthat the rapid decrease in the number of bacteria in E.coli O157:H7 was caused by rapid temperature changes in the freeze-thaw cycle.Low temperature will cause theincrased death of E.coli O157:H7,and low temperature will become the most important factor affecting E.coli O157:H7.The survival time(ttd)of E.coli O157:H7 was significantly different at-14?/+6? and-6?/+6? freeze-thaw cycles(P < 0.001),at-14?/+6? The survival time(ttd)of E.coli O157:H7 was also significantly different under-10?/+6? freezing and thawing conditions(P<0.01).(3)Under different freeze-thaw cycles,relative abundance of Acidobacteria,Chloroflexi,Planctomycetes,Latescibacteriain soil aresignificantly positively correlatedto the survival time(ttd)of E.coliO157:H7.The survival time(ttd)of E.coli O157:H7 was significantly negatively correlated with the relative abundance of Firmicutes.(4)The results of CCA and SPSS analysisRevealed that TN and clay are the main soil physical and chemical properties affecting the survival behavior of E.coli O157:H7.Other physical and chemical properties affecting the survival of E.coli O157:H7 are pH,EC,etc.There was a significant positive correlation betweenttdof E.coli O157:H7 and total nitrogen(TN)(P<0.001),and a significant positive correlation with clay(P<0.05).TN provided nutrients for the survival of E.coli O157:H7.The pores of the soil provide E.coli O157:H7 with an refuge for environmental changes.Results of this study aremeaningfulto better understand the composition and diversity of microbial communities in the soil,to explore the responsesof human pathogens,and to changes in the environmental conditions of the freeze-thaw cycles in the early spring and late autumn in the north.The the current study provides useful background information inassessment of soil quality and design of soil management strategies fora health and sustainable soil ecosystems.