A multi-site, multi-year examination of factors affecting the persistence of attenuated O157- and non-pathogenic Escherichia coli in manure-amended soils in the mid-Atlantic United States

Authors: Sharma, Manan; Millner, Patricia; HASHEM, FAWZY - University Of Maryland Eastern Shore (UMES); Vinyard, Bryan; Handy, Eric; East, Cheryl - Roberts; White, Kathryn; STONEBRAKER, RICHARD - University Of Maryland Eastern Shore (UMES)

Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 3/16/2017
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: The addition of untreated biological soil amendments (BSAs), including dairy cattle manure (DM), poultry litter (PL), and horse manure (HM), to soils provides nutrients for crops in conventional and organic agriculture, but may also introduce enteric pathogens present in manure to crops. The U.S. Food and Drug Administration currently has no objection to an interval of 90 - 120 days between application of untreated BSA and harvest of crops to minimize crop contamination. To assess the factors that influence the persistence of an attenuated E. coli O157:H7 (attO157) and a non-pathogenic E. coli (gEc) in manure-amended soils, 12 different field trials at 3 different sites in the mid-Atlantic U.S. (two in Maryland, one in Pennsylvania) over the course of 4 years (2011-2015) were performed. Our objective was to assess the role that site/soil type, type of BSA, soil management practices, and manure application method have on the survival of attO157 and gEc in agricultural fields. At each site, plots (2x2 m) were unamended (UN), or amended with DM, PL, or HM, and inoculated with 1 L of a combined inoculum of gEC and attO157 at low (4 log10 CFU/mL) or high (6 log10 CFU/mL) concentrations. Amendments were either surface-applied (S) or tilled (T) into soils. In each study, each treatment contained four replicates. At one of the three sites, survival of attO157 and gEC in organic vs conventional soils was compared. Populations of attO157 and gES, measured in log10 CFU/gdw (gram dry weight), were then enumerated using selective differential media for up to or greater than 180 days. Experimental conditions (n=162) for attO157 and gEc were fit to one of six non-linear models. The persistence of attO157 and gEC was then measured by calculating the area under the curve (AUC) using a negative binomial distribution. Significant differences (P < 0.05) in total AUC values for each experimental condition were determined. Site, amendment type, season, soil management, and depth all significantly influenced the persistence of attO157 and gEc. Under most experimental conditions, attO157 and gEc persistence was significantly different (p < 0.05) in manure-amended soils than in unamended soils. In 71% (34/48) of trials, PL-amended soils supported longer durations of E. coli persistence compared to soils amended with other BSA’s, regardless of all other factors. In 40% (29/48) of trials, it took more than 120 days for 95% of the initial E. coli inoculum to die off. Geographic location, soil and specific BSA type can significantly influence the persistence of E. coli in manure-amended soils.