Survival Of E. Coli O157: H7in Soil And Its Relationship With Soil Properties

Enterohemorrhagic Escherichia coli (EHEC) is one of the Shiga Toxinproducing Escherichia Coli (STEC) strains, which can cause a large number of human diseases, including uncomplicated diarrhea, hemorrhagic colitis and hemolytic-uremic syndrome. The well-known Escherichia coli O157:H7(E. coli O157:H7), an important food-borne pathogen, poses great threat to the public health because of its low infective dose (as few as10cells) and its high pathogenicity. Raw fruits and vegetables are main vehicles for transmitting O157:H7via field application of manure or contaminated irrigation water. Accordingly, studying its survival in environmental samples is of great importance to ensure food-safety and reduce its negative environmental impacts.In the present study, laboratory incubation experiments were conducted to determine the growth curve of E. coli O157:H7in Luria-Bertani broth and its survival dynamics in4soils under different land uses and6soils from different regions in China. E. coli O157:H7growth curves exhibit in4stages:the initial lag (0-1h) stage, logarithmic growth stage (1-5h), stationary stage (5-16h) and the aging stage (after cultured16h). The strains in the stationary stage were selected and inoculated into soil samples to study its survival dynamics in the test soils. We found that:(1) The survival of E. coli O157:H7varied in soils but fitted well to the Weibull model.(2) The calculated td values (time needed to reach the detection limit,100colony forming unit per gram soil dry weight) for the tested soils from four different land use types (forest, tea plantation, bamboo grove, and vegetable garden) were between2.07-3.59days, with the longest td being observed in soils from bamboo grove. Stepwise multiple regression analysis revealed that the td values were shorter in sandy, lower pH and lower organic carbon soils.(3) Differences of E. coli O157:H7survival were also observed in6soils collected from Heilongjiang, Shaanxi, Henan, Zhejiang, and Hunan provinces in China from north to south. The td values followed the order of Shaanxi (24.72d)> Henan (19.55d)> Heilongjiang (13.57d)> Zhejiang (10.21d,9.93d)> Hunan (7.28d). Stepwise multiple regression analysis revealed that E. coli0157:H7survival in the test soils was related with soil pH and soil texture.(4) In addition, adjustment of soil pH in the acidic soils changed E. coli0157:H7survival times. The td values increased with soil pH in the soils from Heilongjiang and Hunan provinces. Compared to the original soils, the td values decreased in soils from Zhejiang province after soil pH adjustment. However, the td values did not change obviously with pH in the slightly alkaline soil samples from Shaanxi and Henan provinces.