After the application of organic fertilizers, most soil samples
were neutral or alkaline (Table 2), which reduced the inhibitory
effects described above. The increased organic matter resulted in an
increase of negative charges of soil particles, which decreasedE. coli
adhesion on soil particles, especially at pH≥6[36]. In addition,
soil EC increased as a consequence of organic fertilizer application (Table 2), which indicated higher soil salinity and electrolyte
concentration[26,37]. Liu et al. [31]revealed a decrease inE. coli
adhesion with increasing electrolyte concentrations, because it
became hard forE. colito pass through the diffuse layers on the Fe/Al
(hydro) oxides to access the surface of the Fe/Al (hydro) oxides.
However, the stepwise multiple regression showed that EC negatively affect theE. coliO157:H7 survival in 20 fertilizer-amended
soils (Table 3). It was mainly attributed to the osmotic effect caused
by higher salinity, which might suppress crucial protein synthesis
and lead to a decreased enzyme activity and gene expression[38].
Munro et al. reported that the exposure to high osmolarity would
decrease the efficiency of ribosomal translation kinetics at least
partly regulated by the RpoS gene, which could enhanceE. colisurvival subjected to nutrient starvation[39]. The indirect effect of EC
via WSOC were positive, accounting for 22.9% (Table 4). This indicated that the inhibitory effect of high salinity onE. colisurvival
would not be so high under relatively copiotrophic conditions due
to specific gene expression affected by high salinity, in this mainly
oligotrophic environment[39,40]. It may be meaningful to investigate the gene expression in response to salt stress under different
nutrient level toward a better understanding of theE. coliO157:H7
survival mechanisms at the molecular level