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Title: PERSISTENCE OF ESCHERICHIA COLI O157:H7 IN SOIL AFTER FUMIGATIONS

Author
item Ibekwe, Abasiofiok - Mark
item Grieve, Catherine
item YANG, C. - UNIV WISCONSIN, MILWAUKEE

Submitted to: American Society for Microbiology Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 2/10/2006
Publication Date: 4/25/2006
Citation: Ibekwe, A.M., Grieve, C.M., Yang, C.-. 2006. Persistence of escherichia coli O157:H7 in soil after fumigations. [CD-ROM] American Society for Microbiology Annual Meeting. Orlando, FL.

Interpretive Summary:

Technical Abstract: Long term persistence of Escherichia coli O157:H7 in soil and in the rhizosphere of many crops is relatively unknown. Many groups have voiced concerns about the safety of land application of manure and the potential for food and water contamination by E. coli O157:H7 from agricultural runoffs. 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 two experiments. Plants were grown at 20°C in growth chambers during the first experiment. For the second experiment, soil microcosms were used in the laboratory 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. A direct correlation was determined between the fluorescence threshold cycle (CT) and the starting quantity of E. coli O157:H7 DNA. The detection limit for the real time PCR assay was 2.4 X 103 CFU g-1 E. coli O157:H7. Both fumigants were effective in reducing pathogen concentrations in soil in the short run, but there were no significant long term effects of fumigants on the persistence of pathogens even when fumigants were applied at five times the normal application rate. Persistence of pathogen was consistently higher in sandy soil than clay soil used in this study. 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 suggesting regrowth due to survival of a sub-population within the general population. Both experiments showed that E. coli O157H:7 can persist in the environment for a long period of time, and, even under harsh conditions, the pathogen can persist and may regrow. This provides a very significant pathway for pathogen recontamination in the environment.