Temporal and agricultural factors influence E. coli survival in soil and transfer to cucumbers

Authors: LITT, PUSHPINDER - University Of Delaware; KELLY, ALYSSA - University Of Delaware; OMAR, ALEXIS - University Of Delaware; JOHNSON, GORDON - University Of Delaware; Vinyard, Bryan; KNIEL, KALMIA - University Of Delaware; Sharma, Manan

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/7/2021
Publication Date: 3/11/2021
Citation: Litt, P.K., Kelly, A., Omar, A., Johnson, G., Vinyard, B.T., Kniel, K.E., Sharma, M. 2021. Temporal and agricultural factors influence E. coli survival in soil and transfer to cucumbers. Applied and Environmental Microbiology. https://doi.org/10.1128/AEM.02418-20.
DOI: https://doi.org/10.1128/AEM.02418-20

Interpretive Summary: Poultry litter and other biological soil amendments are commonly used as fertilizers in fruit and vegetable production and can introduce or extend survival of enteric pathogens like E. coli O157:H7 or Salmonella, commonly associated with outbreaks of infections linked to contaminated produce. Results presented here show that longer survival durations of E. coli were shown in soils containing poultry litter, heat-treated poultry pellets, or composted poultry litter covered with black plastic mulch; there was a strong year to year effect due to the different levels of rainfall in each year of the study. Similarly, greater transfer of E. coli to cucumbers from amended soils was associated with combinations of year, amendment and much factors which supported longer survival durations. While nitrate level and soil moisture values on specific days were good predictors of E. coli survival in specific plots, knowledge of year, amendment and mulch type provided the largest predictive value of E. coli survival duration. This research benefits farmers by showing the survival of E. coli in soils can be extended by the addition of several type of biological soil amendments commonly used in organic production of fruits and vegetables, but is also highly dependent on temporal variation in rainfall.

Technical Abstract: Biological soil amendments of animal origin (BSAAO) like poultry litter are used to increase nutrient levels in soils to support the production of fruits and vegetables. Untreated BSAAO like poultry litter may introduce and / or support survival of bacterial pathogens which can transfer to fruits and vegetables and cause foodborne illness. Escherichia coli survival in replicate soil plots (3m2) amended with either poultry litter (PL), composted poultry litter (CPL), heat treated poultry pellets (HTPP), or chemical fertilizer (UN) and transfer to cucumbers in two separate years (2018, 2019) was evaluated. In each year, one-half of the test plots were either covered with black plastic mulch (M) or not (NoM). Each plot was spray-inoculated with 1 L of E. coli TVS 355 (6 log CFU/ml) and cucumber seedlings (Supremo) were planted. The number of days needed to reduce E. coli levels by 4 log CFU (dpi4log) were determined by using a sigmoidal decline model in all combinations of year, amendment, and mulch treatments. Random forest regression and one-way ANOVA (p < 0.05) was used to identify predictors of E. coli survival and transfer to cucumbers from factors including: rainfall, air temperature; soil temperature, moisture, and conductivity; water-extractable carbon, total nitrogen, nitrate, and soluble solids . The combination of year, amendment and mulch were the most prominent predictors of dpi4log (574 %IncMSE) and transfer to cucumbers (0.57 %IncMSE), respectively. In 2018, the largest dpi4log values (97.5 – 106 days) originating from CPL M, HTPP M, PL M, and UN NoM plots were significantly greater than those from CPL NoM and HTTP NoM (28.5 - 49 days) plots; in 2019, HTPP NoM and PL M plots supported larger dpi4log values (85.5 days) were significantly greater than those from CPL NoM, UN M, UN NoM plots (28.5 – 39.5 days). Significant predictors of E. coli survival also included nitrate levels on day 30, soil moisture values on day 40, and soluble carbon levels on day 40 (6.17 %IncMSE) may have been affected by the greater cumulative rainfall observed in 2018 (24.9 in) compared to 2019 (12.6 in). Greater transfer of E. coli to cucumber was also shown to be associated with longer survival durations (dpi4log) of E. coli in plots containing BSAAO.