Influence of Microbial Community Diversity on Survival of Escherichia Coli O157:H7 In Two Contrasting Soils

Survival of Escherichia coli (E. coli) O157:H7 in the environment is a major concern to growers where farms and livestock production are in close proximity and stresses the importance of the development of intervention strategies that minimizes the risk of preharvest contamination. The major objectives of this study were to determine the effects of preplant fumigation treatment on the survival of E. coli O157:H7 in two soils and the effects of indigenous bacterial populations on the survival of this pathogen. A preliminary study was conducted to determine the effects of bacterial diversity on the survival of E. coli O157:H7 in autoclaved and unautoclaved soils. Using the Weibul model, survival curves showed a convex curvature in most of the autoclave soil and a concave curvature in the unautoclaved soil. The basic explanation may be that the convex model presented a quick growth in bacterial population before die off begins and the cells were more susceptible to stress, whereas in the concave model with unautoclaved soil there was a rapid die off in the sensitive population and a more resistant population were left. Real-time PCR and plate counts were used to quantify the survival of E. coli O157:H7 in two contrasting soils. Real-time PCR assays were designed to amplify toxin genes in E. coli O157:H7. Ten days after fumigation, E. coli O157:H7 counts were significantly lower (P = 0.0001) in fumigated soils (normal application rate) than in the non-fumigated. Microbial species diversity as determined by DGGE was significantly higher in clay soil than sandy soil and this resulted in higher initial decline in population in clay soil than in sandy soil. This was consistent with our hypothesis that in most soil systems the use of first-order decline models to describe survival of E. coli O157:H7 may not be the best strategy.