Survival Of Escherichia Coli O157:H7 In Soils Over A PH Gradient In Jilin Province And The Influencing Factors

Escherichia coli O157:H7 is a gram-negative food-borne pathogen which could be transmitted among soil,food and human body.It could cause potential life-threatening illnesses like diarrhea,uremia and other diseases.The pH of soils in Jilin Province decreases from west to east,exhibiting a natural pH gradient zone.In order to better understand the survival mechanism of soil microorganisms,reduce the risk of E.coli O157:H7 outbreak and protect human health,we chose 24 soils with different pH in Jilin Province as experimental soils to study the survival behavior of E.coli O157:H7 and explore the effects of soil physicochemical properties and soil bacterial community on the survival of E.coli O157:H7.In the experiment,we collected soils in different areas of Jilin Province and divided them into four groups based on the distinguished pH value.To be specific,soils with pH?6.5 were weak acidic soils,6.5<pH<7.5 were neutral soils,7.5<pH<8.5 were weak basic soils and those pH?8.5 were strong basic soils.E.coli O157:H7 was inoculated into soils with different pH and the number of bacteria was continuously recorded.Weibull model was used to simulate the time required for the number of E.coli O157:H7 to reach the detection limit?100 CFU/gdw?and other parameters.At the same time,we detected the physical and chemical properties of soil and conducted the 16S rRNA sequencing in soil.Finally,the factors affecting the survival behavior of E.coli O157:H7 in different pH soils and soil microbial community were analyzed.The results showed that the survival time of E.coli O157:H7 in weak acidic,neutral,weak basic and strong basic soils was 61.08 days,72.05 days,76.85 days and18.54 days,respectively.pH is the key factor affecting the survival of E.coli O157:H7.Excessive pH can not only directly destroy the cell metabolism and inhibit the survival of E.coli O157:H7,but also indirectly affect the survival of E.coli O157:H7 by exerting impact on other physicochemical properties of soil?such as WSOC,NH₄⁺-N,water content?and soil microbial structure.In addition to pH,soil physicochemical properties such as NO₃^--N,clay,NH₄⁺-N also inhibited the survival of E.coli O157:H7,while TP promoted the survival of E.coli O157:H7.Biological factors were also linked to the survival of E.coli O157:H7.The diversity of soil microbial community was negatively correlated with the survival of E.coli O157:H7.Proteobacteria in soils promoted the survival of E.coli O157:H7,while Acidobacteria constrained the survival of E.coli O157:H7.To sum up,the soil used in the experiment were far away from each other and the physical and chemical properties and microbial community structure are differed largely.So it is reasonable to make comprehensive consideration including all aspects of influence factors when evaluating the survival of E.coli O157:H7 in soils over a pH gradient.