PERSISTENCE OF ESCHERICHIA COLI O157:H7 IN RHIZOSPHERE AND NON-RHIZOSPHERE SOILS AFTER FUMIGATION

Authors: Ibekwe, Abasiofiok - Mark

Submitted to: International Union of Microbiological Societies Proceedings/Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2005
Publication Date: 7/1/2005
Citation: Ibekwe, A.M. 2005. Persistence of Escherichia coli O157:H7 in rhizosphere and non-rhizosphere soils after fumigation. International Union of Microbiological Societies Proceedings/Abstracts. Page 18.

Interpretive Summary:

Technical Abstract: Agricultural soils are fumigated to provide effective control of nematodes and soil-borne pathogens in preparation for planting high value cash crops. Animal manure has been applied to agricultural land with little or no regulation. Many groups have voiced concerns about the safety of land application of manure and the potential for food and water contamination by Escherichia coli (E. coli) O157:H7 from agricultural runoffs. Methods: Multiplex fluorogenic PCR was used in conjunction with plate counts to quantify E. coli O157:H7 in soil after fumigation with methyl bromide (MeBr) and methyl iodide (MeI). E. coli O157:H7 strain 72 with green fluorescent protein (pGFP) was used for this study. The plants were grown at 20°C with 70% relative humidity and a photoperiod consisting of 16 h of light and 8 h of darkness in the growth chamber during the first experiment. For the second experiment, soil microcosms was used in the lab without plants and spiked with two fumigants. Primers and probes were designed to amplify and quantify the Shiga-like toxin 1 (stx1) and 2 (stx2) genes and the intimin (eae) gene of E. coli O157:H7. Results: A direct correlation was determined between the fluorescence threshold cycle (CT) and the starting quantity of E. coli O157:H7 DNA. The detection limit was 2.4 X 102 CFU ml-1 E. coli O157:H7 based on plate counts. Both fumigants were effective in reducing pathogen concentrations in soil before planting and in microcosm. Persistence of pathogen was consistently higher in sandy soil than clay soil. Regression models showed that persistence of pathogen in the growth chamber study followed a linear model while that of the microcosm followed a curvilinear model. Conclusions: Both experiments showed that E. coli O157H:7 can persist in the environment for long period of time, and under favorable growth conditions the pathogen can regrow. This provides a very significant pathway for pathogen recontamination in the environment.