Factors affecting Salmonella Newport survival in soil and subsequent transfer to spinach plants

Authors: SHAH, MANOJ - North Dakota State University; BRADSHAW, RHODEL - US Department Of Agriculture (USDA); Handy, Eric; East, Cheryl - Roberts; BERGHOLZ, TERESA - North Dakota State University; Sharma, Manan

Submitted to: International Association for Food Protection
Publication Type: Abstract Only
Publication Acceptance Date: 3/15/2019
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Introduction: Biological soil amendments such as untreated poultry litter can harbor pathogens like Salmonella leading to potential transfer from soils to produce. Heat-treated poultry pellets (HTPP) can provide produce growers a slow release fertilizer with a minimized risk. However, little is known about the impact of HTTP-amendment on survival of Salmonella in soil. Purpose: The purpose of this experiment was to assess the impact of HTPP as an amendment on the survival of Salmonella Newport in soil, and the contribution of factors, such as irrigation, presence/absence of spinach plants, rpoS gene, and potential formation of viable but non-culturable cells on survival. We also determined the populations of S. Newport surviving on spinach leaves after simulated transfer. Methods: S. Newport wild-type (WT) and rpoS-deficient ('rpoS) strains were drip-inoculated in HTPP-amended and unamended soil in planters (61cmx17.8cmx15.6cm) and seeds of spinach plants were sown. Survival of S. Newport was quantified by culture methods and PMA-qPCR over 91 days. A simulated ‘splash’ transfer of S. Newport from contaminated soil to spinach leaves was evaluated at 35 and 63 days post-inoculation (dpi) and survival on spinach leaves were quantified for 48 h. Results: S. Newport WT and 'rpoS reached the limit of detection (1.0 log CFU/gdw) in unamended soil at 35 dpi, whereas 2-4 log CFU/gdw was observed for both strains at 91 dpi in HTPP-amended soil. No significant differences in survival were observed between the strains. Populations determined by PMA-qPCR and culture methods were similar (p>0.05), as was survival in soils with or without spinach plants. Higher populations of S. Newport from HTTP-amended soil transferred to and survived on spinach leaves compared to those from unamended soils (p<0.05). Significance: HTTP-amended soils provided a favorable environment for Salmonella Newport survival in soils and transfer to spinach plants when introduced via irrigation during spinach cultivation when compared to unamended soils.