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Title: Persistence of escherichia coli O157:H7 and its mutants in soils

item MA, JINCAI - University Of California
item Ibekwe, Abasiofiok - Mark
item YI, XUAN - University Of Wisconsin
item WANG, HAIZHEN - Zhejiang University
item YAMAZAKI, AKIHIRO - University Of California
item CROWLEY, DAVID - University Of California
item YANG, CHING-HONG - University Of Wisconsin

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2011
Publication Date: 8/3/2011
Citation: Ma, J., Ibekwe, A.M., Yi, X., Wang, H., Yamazaki, A., Crowley, D.E., Yang, C. 2011. Persistence of escherichia coli O157:H7 and its mutants in soils. PLoS One. 6(8):1-8.

Interpretive Summary: Escherichia coli O157:H7 is an important human pathogen that is responsible for about 73,480 cases of disease per year, among which; there are more than 1,800 cases of hospitalizations and 52 deaths. The infectious threshold of E. coli O157:H7 is very low, and ingestion of as low as 10 cells is enough to cause severe gastrointestinal illness. Shiga toxin genes are the most important factors in E. coli O157:H7 responsible for disease outbreaks and the bacterium is known to survive in the environment for months. In this study, we determined the role of shiga toxin genes in the survival of E. coli O157:H7 in three soils using mutants with deletions of the different toxin genes. E. coli survived more than six months in clay soil while survival in sandy soil was significantly shorter. The results of this research will be used by growers and researchers in the pre-harvest leafy green production environment.

Technical Abstract: The persistence of Shiga toxin-producing E. coli O157:H7 in the environment poses a serious threat to public health. However, the role of Shiga toxins and other virulence factors in the survival of E. coli O157:H7 is poorly defined. The aim of this study was to determine if the virulence factors, stx1, stx2, stx1–2, and eae in E. coli O157:H7 EDL933 play any significant role in the growth of this pathogen in rich media and in soils. Isogenic deletion mutants that were missing one of four virulence factors, stx1, stx2, stx1–2, and eae in E. coli O157:H7 EDL933 were constructed, and their growth in rich media and survival in soils with distinct texture and chemistry were characterized. The survival data were successfully analyzed using Double Weibull model, and the modeling parameters of the mutant strains were not significantly different from those of the wild type. The calculated Td (time needed to reach the detection limit, 100 CFU/g soil) for loamy sand, sandy loam, and silty clay was 32, 80, and 110 days, respectively. It was also found that Td was positively correlated with soil structure (e.g. clay content), and soil chemistry (e.g. total nitrogen, total carbon, and water extractable organic carbon). The results of this study showed that the possession of Shiga toxins and intimin in E. coli O157:H7 might not play any important role in its survival in soils. The double deletion mutant of E. coli O157:H7 (stx1 2stx2 2) may be a good substitute to use for the investigation of transport, fate, and survival of E. coli O157:H7 in the environment where the use of pathogenic strains are prohibited by law since the mutants showed the same characteristics in both culture media and environmental samples.