T7-07 Association of Fresh Produce Food Safety Hazard with Growth and Persistence of Escherichia coli in Soils Amended with FSMA-compliant Heat-treated Manure

Tuesday, July 11, 2017: 3:30 PM
Room 15 (Tampa Convention Center)
Patricia Millner , USDA ARS Environmental Microbial and Food Safety Laboratory , Beltsville , MD
Kathryn White , U.S. Department of Agriculture–ARS , Beltsville , MD
Herbert Clark , University of Maryland Eastern Shore , Princess Anne , MD
Fawzy Hashem , University of Maryland Eastern Shore , Princess Anne , MD
Manan Sharma , USDA ARS Environmental Microbial and Food Safety Laboratory , Beltsville , MD
Introduction: Heat-treated, manure-based amendments are used for soil conditioning/fertilizing organically and conventionally grown fresh leafy greens and root crops. The risk of contamination from growth, persistence, and ultimately transfer of fugitive fecal bacterial pathogens to fresh produce upon contact between these preplant and side-dress amendments and crops is uncertain. Determining the impacts from use of FSMA-compliant soil amendments to grow produce is critical for devising science/risk-based food safety practices.

Purpose: This study investigated associations between heat-treated manure-based soil amendments and growth, survival, and transfer of Escherichia coli to spinach and radish.

Methods: Two randomized complete block field experiments (n=4 replications each) with soil amendments [composted poultry litter, composted dairy manure, vermicomposted dairy manure, heat-treated poultry litter pellets (PLP), and urea (control)] were conducted. Plots, spray-inoculated with a three-strain cocktail of rifampicin-resistant generic E. coli isolates (gEcr), were tilled, seeded, overhead irrigated, and assayed 14 times (0 to 91 days) for gEcr. Spinach leaves and radish were assayed (28 to 84 days) for gEcr. Radish globes were washed, trimmed, sanitized (10 to 50 mg/L HOCl, pH6.5) for five minutes, then neutralized, and assayed for gEcr.

Results: Populations of gEcr in plots were ~ three log CFU/g soil (day 0) and increased 10- to 100-fold (day 1) for compost/urea and PLP treatments, respectively. The gEcr population persisted 84+ days in compost- and PLP-amended plots, but these organisms were barely detectable in urea treatments (day 28). Average gEcr populations on radish from compost and PLP plots were 1.17 and 3.29 log MPN/globe, respectively, and significantly (P<0.05) greater than on spinach leaves. Serial washings removed visible soil from radish globes (n=72) and reduced, but did not completely eliminate, gEcr from trimmed, chlorine-sanitized globes (n=48).

Significance: Heat-treated PLP, unlike composted manures or urea, promoted significant growth of gEcrin soil and transfer onto produce in direct contact with soil. Additional studies are needed to determine quality factors in commercially available heat-treated PLP responsible for this growth promotion.