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P3-50 The Effect of Soil Management on the Persistence of Escherichia coli and Listeria spp. in Manure-amended Soils in the Northeast United States

Wednesday, July 12, 2017
Exhibit Hall (Tampa Convention Center)
Panagiotis Lekkas , University of Vermont , Burlington , VT
Manan Sharma , USDA ARS Environmental Microbial and Food Safety Laboratory , Beltsville , MD
Deborah Neher , University of Vermont , Burlington , VT
Thomas Weicht , University of Vermont , Burlington , VT
Patricia Millner , USDA ARS Environmental Microbial and Food Safety Laboratory , Beltsville , MD
Catherine Donnelly , University of Vermont , Burlington , VT
Introduction: Enterohemorrhagic Escherichia coli and Listeria monocytogenes can contaminate leafy greens through inappropriately managed raw manure applied to soils. Current FDA guidance includes calling for additional scientific data to determine the appropriate interval between application of manure and harvest of crops grown in manure-amended soils to minimize risk of human illness.

Purpose:  To determine persistence of E. coli and Listeria spp. populations in sandy and loamy soils amended with dairy-manure solids (DS) in Vermont.

Methods: One liter of a three-strain inoculum (TVS353,TVS354, and TVS355) of rifampicin-resistant E. coli (rEc) (six log CFU/ml) was sprayed onto field plots (2m2) of either loamy sand (L) or sandy (S) soils amended with DS or no manure (NM). DS was either tilled into soil or spread on the surface. Survival of inoculated rEc, naturally present E. coli (nEC) and Listeria spp. in DS in untilled and tilled plots were quantified over 56 days postinoculation (dpi) by direct plating or MPN.

Results: By 56 dpi, in surface plots, rEc populations declined by 3.65 to 3.69 log CFU/g and 3.05 to 3.11 log CFU/g in L and S soils, respectively. In tilled plots, rEc populations declined by 2.27 to 2.33 and 2.08 to 2.14 log CFU/g in L and S soils, respectively. In L and S soils, rEc populations in surface NM declined to undetectable levels by 14 and 28 dpi, respectively. Overall, Listeria spp. populations increased by 0.05 to 0.96 log MPN/g by day 56, and Listeria spp. were present in both NM and DM-amended soils. The nEcpopulations declined by 1.15 to 1.60 log CFU/g by 56 dpi.

Significance: In comparison to studies conducted in the two previous years at the same sites, rEc populations declined more rapidly by seven dpi in this iteration. Results presented from this year’s study indicates that soil tillage influences survival of E. coli as much as dairy manure amendment.

Back to: Poster Session 3 – Low-water Activity Foods, Packaging, Produce, Microbial Food Spoilage, Antimicrobials, Laboratory and Detection Methods, Water
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