Survival of Escherichia coli O157:H7 in soils along a natural pH gradient

Persistence of E. coli O157:H7 (EcO157) in soils from different places was widely reported, while its survival behavior in soils over a pH gradient was yet to be investigated. In the current study, a total of 24 soil samples were collected along a natural pH gradient, and the soils were classified into weak acidic soil (pH < 6.5), neutral soil (6.5 < pH < 7.5), weak basic soil (7.5 < pH < 8.5), and strong basic soil (8.5 < pH < 10). Soil physical and chemical properties were determined using standard methods, and bacterial communities were characterized by next generation high throughput sequencing protocol. EcO157 cells were inoculated into those soils and the survival profiles were investigated. The influencing factors affecting the survival behavior of EcO157 were analyzed by multivariate statistical analysis. The results showed that the average survival time of EcO157 in weak acidic, neutral, weak basic and strong basic soils was 61.08, 72.05, 76.85 and 18.54 days, respectively. The survival time in strong basic soils was significantly less than those in the other three soil groups. Results of both stepwise multiple regression and Mental tests revealed that soil physicochemical properties such as NO ₃ ^- -N, clay content, and NH ₄ ⁺ -N negatively linked to the survival of EcO157, while TP was positively correlated to the survival of EcO157 ( P <0.05). Stepwise multiple regression showed that microbial community diversity was negatively correlated with the survival of EcO157, while relative abundances of Proteobacteria and Acidobacteria were positively and negatively correlated to the survival of EcO157, respectively. Our study highlighted the role of pH in the survival of EcO157 in soils. Both co-occurrence networks analysis and structural equation model results showed that pH was a key factor that could directly and indirectly via bacterial community influence the survival of EcO157. Our data coupled with the findings of others might be of great helpful in evaluation, control, and reduction of the potential health risk associated with EcO157 in soils along a natural pH gradient.