Submitted to: Current Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2012
Publication Date: 6/2/2012
Citation: Rothrock Jr, M.J., Frantz, J., Burnett, S.E. 2012. Effect of volumetric water content and clover (Trifolium incarnatum) on the survival of Escherichia coli O157:H7 in a soil matrix. Current Microbiology. 65(3):272-283. Interpretive Summary: The survival of Escherichia coli O157:H7 within soils is a vital issue for minimally processed, ready-to-eat and organic vegetable production systems. Therefore, environmental factors that control the survival of E. coli O157:H7 in these soils must be studied in greater detail. The goal of this study was to determine the effect of one major physical factor (soil moisture) and one major cropping system factor (growth of the organic cover crop, clover) on the survival of E. coli O157:H7 in soils. Using both traditional plate counts and molecular-based quantification methods, the survival of E. coli O157:H7 was significantly lower in extremely moist (near water holding capacity) as compared to more moderate (~50% of water holding capacity) moisture regimes. Additionally, the growth of clover also significantly reduced E. coli O157:H7 survival, as compared to unplanted soil. Given the significant effect of clover on E. coli O157:H7 survival, future work should concentrate on the specific mechanisms of inhibition by clover exudates; ultimately leading to the development of crop rotations/production systems to improve pre-harvest food safety and security in minimally processed, ready-to-eat and organic production systems.
Technical Abstract: Due to the inevitable introduction of zoonotic manure-born human pathogens, such as Escherichia coli O157:H7, into minimally processed, ready-to-eat and organic vegetable production systems via animal manure-based organic fertilizer, studies aimed at understanding the survival dynamics of these pathogens within the soils of these systems are paramount. Therefore, a study was conducted to determine the survival of E. coli O157:H7 in soil matrices subjected to two variable environmental stressors: (1) soil moisture as determined by real-time monitored volumetric water content (25% or 45% VWC), and (2) the growth of clover (planted or unplanted). During the seven week study, molecular-based qPCR analyses revealed that E. coli O157:H7 survival (determined by targeting the uidA gene) was significantly lower in soils maintained at either near water holding capacity (45% VWC) or under clover growth. The significant reduction under clover growth was only observed when E. coli populations were determined relative to all bacteria (as determined by targeting the 16S gene), indicating the need to further study the competition between E. coli O157:H7 and the total bacterial community in minimally processed or organic soils. Given the significant effect of clover on E. coli O157:H7 survival under different moisture conditions, this work highlights the antimicrobial potential of clover exudates in arable soils, and future work should concentrate on their specific mechanisms of inhibition; ultimately leading to the development of crop rotations/production systems to improve pre-harvest food safety and security in minimally processed, ready-to-eat and organic production systems.