Differential survival of generic E. coli and Listeria spp. in Northeastern U.S. soils amended with dairy manure compost, poultry litter compost, and heat-treated poultry pellets and fate in raw edible radish crops

Authors: LIMOGES, MARIE - University Of Vermont; NEHER, DEBORAH - University Of Vermont; WEICHT, THOMAS - University Of Vermont; Millner, Patricia; Sharma, Manan; DONNELLY, CATHERINE - University Of Vermont

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/29/2021
Publication Date: 12/2/2021
Citation: Limoges, M.A., Neher, D., Weicht, T.R., Millner, P.D., Sharma, M., Donnelly, C. 2021. Differential survival of generic E. coli and Listeria spp. in Northeastern U.S. soils amended with dairy manure compost, poultry litter compost, and heat-treated poultry pellets and fate in raw edible radish crops. Journal of Food Protection. https://doi.org/10.4315/JFP-21-261.
DOI: https://doi.org/10.4315/JFP-21-261

Interpretive Summary: Biological soil amendments of animal origin (manure) can provide nutrients to soils to aid in the growth of fruit and vegetable crops. Amendments can be composted or heat-treated to reduce the risk of foodborne pathogen contamination to the fruits and vegetables, which can lead to cases of foodborne illness. While composting and heat treatment of amendments can reduce the risk of foodborne pathogen transfer to crops in the field, they still can provide nutrients and/or increase the water-holding capacity of soils, which can aid pathogen survival in soils contaminated by irrigation water or wildlife feces. The objective of this research was to determine the duration of survival of non-pathogenic Escherichia coli in Vermont soils containing treated soil amendments, including composted poultry litter, composted dairy manure, or heat-treated poultry litter pellets. In addition, E. coli transfer from soil to radishes, a rapidly maturing, high soil contact crop, was evaluated. In general, E. coli survived for longer durations and at higher levels in soils containing composted poultry litter or heat-treated poultry pellets compared to soils containing composted dairy manure or soils with no compost. More E. coli transferred to radishes from soils containing composted poultry litter than from soils containing other amendments. Extending the time between treated amendment application to soils and harvest of root crops also needs further examination to reduce the risk of pathogen transfer to harvested crops, particularly for crops grown in soils amended with treated manure-based products. Overall, this research highlights for extension specialists, producers and growers the need for appropriate mitigation practices to reduce the risk of produce contamination on high soil-contact crops, like radishes, when specific types of treated manure-based amendments are used to aid fertility and productivity.

Technical Abstract: Composted or heat-treated manure can be added to soils to provide nutrients for fresh produce. These products lower the risk of pathogen contamination to fresh produce than raw animal manures; however, meteorological conditions, geographic location, soil characteristics, and bacterial abundance can influence the presence of pathogenic bacteria, or their indicators (e.g., generic E. coli) and allow potential for produce contamination. Replicated field plots of loamy (L) or sandy (S) soils were tilled and amended with dairy manure compost (DMC), poultry litter compost (PLC), or no compost (NoC) over two different field seasons, and non-composted heat-treated poultry pellets (HTPP) during the second field season. Plots were inoculated with a three-strain cocktail of rifampicin-resistant E. coli (rE.coli) at levels of 8.7 log CFU/m2. Direct plating and most probable number (MPN) methods measured the persistence of rE.coli and Listeria spp. in plots through 104 days post-inoculation (dpi). Greater abundance of rE. coli was observed in PLC plots in comparison to DMC plots and NoC plots during year 1 (P < 0.05). Similar trends were observed for year 2, where rE. coli survival was also greater in HTPP amended plots (P < 0.05). Survival of rE. coli was independent of soil type, soil temperature, and water potential. Listeria spp. were found in NoC plots, but not in plots amended with HTPP, PLC or DMC. Radish data demonstrates that PLC treatment promoted the greatest level of rE.coli translocation when compared to DMC and NoC treatments (P < 0.05). These results are similar studies conducted in other regions of the US and informs Northeast produce growers that composted and non-composted poultry-based Biological Soil Amendments of Animal Origin (BSAAO) supports greater numbers and longer persistence of rE. coli in field soils. This has the potential to impact the food safety risk of edible produce grown in BSAAO amended soils as a result of pathogen contamination.