Effect of Volumetric Water Content and Crimson Clover (Trifolium incarnatum) Growth On the Survival of Escherichia Coli O157:H7 In a Soil Matrix.

The application of manure as an organic amendment has the potential to introduce a host of manure-borne zoonotic pathogens to the fertilized agricultural soils.  In order to determine the potential food safety/security issues with these management practices, the survival of zoonotic pathogens in the soil in relation to a variety of environmental and crop rotation stimuli must be better understood.  Therefore, in this study, avirulent Escherichia coli O157:H7 was inoculated into pots containing a soil mixture (~10^8 CFU/g) maintained at a constant low or high volumetric water content (VWC: ~25% and 45% v/v, respectively), both with and without a common organic production cover crop, crimson clover (Trifolium incarnatum).  To determine the effect of these environmental and crop stimuli on the survival of this manure-borne zoonotic pathogen, weekly Escherichia coli O157:H7 concentrations were calculated using qPCR assays targeting the E.coli-specific beta-D-glucuronidase (uidA) gene.  Growth rates for the crimson clover under the different moisture regimes were also assessed and compared to E. coli inactivation rates to determine any potential correlations.  There were two major findings from this study: (1) for both the unplanted and planted treatments, E. coli concentrations were always significantly higher in the low VWC (25%) as compared to the high VWC (45%) treatment; (2) the presence of crimson clover resulted in significantly lower E. coli concentrations throughout the experiment as compared to the unplanted treatments. For the crimson clover treatments, there was a significant correlation between the growth rate of the clover and the inactivation rate of E. coli.  These findings indicate that lower moisture soils favor the survival of E. coli, and that there may be added bacteriocidal benefits to including crimson clover in an organic production crop rotation.