ARS | Publication request: The effect of soil pasteurization on the persistence of E. coli O157:H7 and Salmonella spp. in fallow and spinach-grown soil

Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: March 2, 2011
Publication Date: August 1, 2011
Citation: Ingram, D.T., Sharma, M. 2011. The effect of soil pasteurization on the persistence of E. coli O157:H7 and Salmonella spp. in fallow and spinach-grown soil. International Association for Food Protection Proceedings. T1-09.

Technical Abstract: Introduction: The survival and persistence of E. coli and Salmonella in soils is dependent on many factors, including the presence of other microorganisms (fungi, bacteria, nematodes) and other nutrient sources, such as root exudates from growing plants. Practices, like soil fumigation, which are targeted to eliminate phytopathogens, may also affect the survival of bacterial of foodborne pathogens in soils. Purpose: This study investigated the effect of soil pasteurization on the persistence of E. coli O157:H7 and Salmonella spp. in both fallow and soils containing baby spinach plants. Methods: Sandy-loam soils (pasteurized or non-pasteurized) were either planted with baby spinach seeds or remained fallow and maintained under growth chamber conditions (14 h photoperiod at 18oC and 10 h at 13oC, 75% humidity). After two weeks, all soils were inoculated with irrigation water containing both E. coli O157:H7 and Salmonella at a population of 5 log CFU/g. Soils were analyzed weekly and enumerated on appropriate selective media to determine E. coli O157:H7 and Salmonella counts. Regression modeling was used to compare treatment effects by comparing the respective rates of decline (kmax = log CFU/g/day ) for E. coli O157:H7 and Salmonella populations. Results: Salmonella populations declined at either a significantly (P< 0.05) slower or the same rate than E. coli O157:H7. In fallow soil, both E. coli and Salmonella populations declined more rapidly in non-pasteurized soil (0.31 and 0.28, respectively) than in pasteurized soil (0.28 and 0.23, respectively). The introduction of baby spinach plants did not significantly contribute to the survival of either E. coli O157:H7 or Salmonella populations as compared to fallow soils. Significance: Pasteurized soils may create a niche for the persistence of transient populations of E. coli O157:H7 and Salmonella spp that may not exist in non-pasteurized soils. The presence of spinach plants did not enhance the survival of either pathogen in soil.