Estimating the stability of Escherichia coli O157:H7 survival in manure-amended soils with different management histories.

The objective of this study is to describe survival of Escherichia coli O157:H7 populations in manure-amended soils in terms of population stability, i.e. the temporal variation around the decline curve, in relation to soil characteristics indicative of soil health. Cow manure inoculated with E. coli O157:H7 was mixed with 18 pairs of organically and conventionally managed soils (10% of manure, kg kg(-1)). For four of the soil pairs, also three different manure densities (5%, 10% and 20%) were compared. All soil-manure mixtures were incubated for 2 months, and population densities of E. coli O157:H7 were quantified weekly. De-trending of survival data was done by modified logistic regression. The residual values were used to assess variation in the changes of E. coli O157:H7 populations by performing the approximate entropy (ApEn) procedure. The term irregularity is used to describe this variation in ApEn literature. On average, the decline of E. coli O157:H7 was more irregular in conventional and loamy soils than in organic and sandy soils (P < 0.05). Multiple regression analysis of irregularity of E. coli O157:H7 survival on 13 soil characteristics showed a positive relation with the ratio of copiotrophic/oligotrophic bacteria, suggesting greater instability at higher available substrate concentrations. Incremental rates of manure application significantly changed the irregularity for conventional soils only. Estimation of temporal variation of enteropathogen populations by the ApEn procedure can increase the accuracy of predicted survival time and may form an important indication for soil health.