2.2. Inoculation and sampling
In China, most E. coli O157:H7 infections occur in summer [3,4]. The summer mean temperature in the test area (Shandong and Zhejiang province) is about 25.2 ◦C and 26.2 ◦C, separately [17,18]. Hence, the simulation experiments were performed at a fixed temperature (25 ± 1 ◦C) to study E. coli O157:H7 survival in soils. Before the inoculation experiment, the soil samples were removed from 4 ◦C storage and incubated in a darkroom at 25 ± 1 ◦C for 5 days to activate the soil microbial communities. E. coli O157:H7 derived from E. coli O157:H7 EDL933 (ATCC 43,895) was used as
the test bacterial strain [9]. Its growth curve in Luria–Bertani (LB) broth (Becton Dickinson, NJ, USA) and survival in soils with distinct
textures were identical to those of the non-induced wild-type
strain [19].