In addition, relatively nutrient-rich soils had a positive selection
for bacteria with potentially high growth rates likeE. coliO157:H7
[6]. The survival time (td)ofE. coliO157:H7 was significantly
increased in fertilizer-amended soils (Figs. 1 and 2). Stepwise multiple regression analysis revealed that the higher WSOC and NO3
−-N
contents contributed to the longerE. coliO157:H7 survival times in
fertilizer-amended soils (Table 3), which was consistent with previous studies[6,26]. It is mainly because carbon and nitrogen are
two essential components of soil microbes. At the same time, relatively sufficient energy sources and nutrients in soil might decrease
the competition between indigenous microorganisms and introduced pathogens[10,19]. Moreover, the increased nutrients would
enhance the horizontal transfer of genetic resistance elements and
therefore increases the frequency of E. coliresistance to antibiotics, such as nalidixic acid, streptomycin and ampicillin[41]. The
redundant NO3
−
-N introduced by organic fertilizer application may
not only enhanceE. coliO157:H7 survival and antibiotic resistance
but also may leach down through the soil into the groundwater
and cause eutrophication and the spread of antibiotic resistant
genes[41]. Hence, in practical operations, the quantity and the timing of fertilization should be controlled exactly and optimally
to balance the fertility improvement and ecological/health risk.
Besides, numerous studies have revealed the relationship between
gut pathogens such asE. coliO157:H7 and a number of reactive
intermediates from the nitrogen cycle in mammals[42,43]. This is
still unclear in soil, which deserves further investigation