Persistence of E. coli O157:H7 in Frozen Soils: Role of Freezing Temperature

Abstract

Soilborne pathogen infections are increasingly reported globally in recent years. Infectious agents have contaminated most of seasonal frozen zone and have been found in permafrost due to the effects of intensified human activities on global warming. Therefore, in regard to sustainable agriculture, it is particularly important to assess the environmental behavior of those pathogens in frozen soils. Due to high pathogenicity and low infection threshold, E. coli O157:H7 (EcO157) is a worldwide public health concern, and recent studies have focused more on its fate in the environment. The survival of this serotype in a large variety of environmental media under temperature above 0 °C has been investigated, while its persistence in frozen soils has received less attention. In this study, we collected soils with different textures from a seasonally frozen zone in northeast China and investigated the persistence of EcO157 in soils at freezing temperatures (−5 °C and −15 °C) and moisture content (30% and 60% water holding capacity (WHC)) of the soils. By fitting the survival data with a Weibull model, we obtained three parameters: first log reduction time (δ in days), survival curve shape parameters (p), and monthly average reduction in EcO157 (MAR, log·gdw−1·mon−1). The results showed that temperature has a major impact on persistence, while moisture content has less effect on the survival of EcO157. Further multi-variable analysis revealed that the physical and chemical properties (e.g., sand fraction) of soil play an important role in survival. Certain bacterial groups are significantly correlated with the survival of EcO157 in frozen soils at −5 °C but not for the ones incubated at −15 °C. Our data could provide background data to evaluate the health risk associated with EcO157. The results could be helpful to improve sustainable soil practices and to develop regulations and policies aiming to achieve sustainable agriculture.