Survival and transfer of Escherichia coli to fresh produce from organically managed soils amended with poultry litter

Introduction Poultry litter (PL) compost and heat-treated PL-pellets (PP) are common organic fertilizer/soil amendments in specialty crop production and soil health management. However, such products may enhance survival and persistence of foodborne pathogens and their transfer to fresh produce. Methods A replicated ( n = 4) 2-year, randomized complete block field-plot inoculated-challenge study, with PL treatments (composted APL and PP) and cover crop/soil placement, was conducted to assess soil persistence/transfer of generic g E.coli rif-R to cantaloupe, cucumber, spinach, and table radish, in cover-cropped USDA-National Organic Program (NOP) 8-years managed as certified plots. Amended soils were analyzed monthly for E. coli up through 90-120-day NOP required wait periods between PL application and produce harvest. Cantaloupe, cucumber, spinach, and table radish, grown compliant with NOP standards, were assayed at harvest for pathogens ( Salmonella, Listeria monocytogenes, Staphylococcus aureus ) and g E. coli . Results and discussion All amended, inoculated soils were positive for the inoculated E. coli (6-log MPN/g) immediately after inoculation. At 90 dpi, all plot soils were positive for the inoculated g Ec rif-R ; by 120 dpi, g Ec rif-R concentrations in soils declined significantly ( p < 0.05) both in 2018 and 2019. No other pathogens ( Salmonella, Listeria monocytogenes, Staphylococcus aureus ) were detected at 0 or 90 dpi in plot soils. Generic Ec rif-R was detected on four of 16 cantaloupes, four of 16 cucumbers from APL plots; four of 20 radish bulbs from till incorporated and four from subsurface-applied APL tested positive for g Ec rif-R at 90 dpi. By 120 dpi, only two spinach plants ( n = 20) were positive from subsurface APL plots; no other pathogens or g Ec rif-R were recovered for any crops in 2018–2019. Significant, consistent declines and decreasing survival throughout the growing seasons in populations of inoculated E. coli in soil, resulted in very low detection on any unwashed produce by 90 and 100 dpi in accord with NOP manure amendment-to-harvest wait times. Exposure to a combination of environmental conditions, including soil moisture, splash transfer of soil to produce, and temperatures (soil and air), impact E. coli populations in tilled and subsurface PL product-amended soils and on produce managed in compliance with organic production requirements.