Survival of Escherichia coli O157:H7 in Soils Along a Natural pH Gradient

Escherichia coli O157:H7 (EcO157) is a Gram-negative foodborne pathogen capable of transmitting between soil, food, and humans, posing a threat to human health. The soil pH in Jilin Province decreases gradually from west to east, exhibiting a natural pH gradient zone. Persistence of EcO157 in soils from different places was widely reported, while its survival behavior in soils over a pH gradient is yet to be investigated. In the current study, a total of 24 soil samples were collected along a natural pH gradient. 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). 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 that in the other three soil groups. Soil physicochemical properties such as NO₃^--N and NH₄⁺-N were negatively linked to the survival of EcO157, while total phosphorus (TP)was positively correlated to the survival of EcO157 (p < 0.05). The microbial community α diversity index was negatively correlated with the survival of EcO157, while relative abundance of Proteobacteria and Acidobacteria was positively and negatively correlated to the survival of EcO157, respectively. Both co-occurrence network analysis and structural equation model results showed that pH was a key factor that could directly and indirectly influence the survival of EcO157 via the bacterial community. Our data coupled with the findings of other studies might be of great help in the evaluation, control, and reduction of the potential health risk associated with EcO157 in soils along a natural pH gradient.