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Title: Soil pasteurization effects on the persistence of E. coli O157:H7 and Salmonella spp. in fallow and spinach-grown soil

Author
item Ingram, David
item Sharma, Manan

Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: 3/21/2011
Publication Date: 4/27/2011
Citation: Ingram, D.T., Sharma, M. 2011. Soil pasteurization effects on the persistence of E. coli O157:H7 and Salmonella spp. in fallow and spinach-grown soil . BARC Poster Day.

Interpretive Summary:

Technical Abstract: The survival and persistence of E. coli and Salmonella in soils is dependent on many factors, including the presence of indigenous microbiota (fungi, bacteria, nematode) and nutrient sources, such as root exudates from growing plants. Soil pasteurization practices, like fumigation, are targeted to eliminate phytopathogens but may also affect the survival of bacterial foodborne pathogens in soils. 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. 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 to achieve a population density 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. 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 at faster rates 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. Pasteurized soils may be a niche for the persistence of transient populations of E. coli O157:H7 and Salmonella spp that may not persist in non-pasteurized soils. The presence of spinach plants did not enhance the survival of either pathogen in soil.