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.