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United States Department of Agriculture

Agricultural Research Service

Research Project: Protection of Food and Water Supplies from Pathogen Contamination Title: Persistence of Escherichia coli O157:H7 in major leafy green producing soils

Authors
item Ma, Jincai -
item IBEKWE, ABASIOFIOK
item Crowley, David -
item Yang, Ching-Hong -

Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 2, 2012
Publication Date: October 2, 2012
Repository URL: http://www.ars.usda.gov/SP2UserFiles/Place/53102000/pdf_pubs/P2378.pdf
Citation: Ma, J., Ibekwe, A.M., Crowley, D.E., Yang, C-H. 2012. Persistence of Escherichia coli O157:H7 in major leafy green producing soils. Environmental Science and Technology. 46:12154-12161.

Interpretive Summary: Escherichia coli O157:H7 is a food-borne pathogen that causes watery diarrhea and sometime death. Undercooked beef is believed to be the major cause of E. coli O157:H7 infection. However, accumulating evidence has shown that fresh produce serves an important vehicle for the transmission of this pathogen. In this study, survival of E. coli O157:H7 in 32 soils (16 organic, 16 conventional) from California (CA) and Arizona (AZ) was investigated. Our data showed that E. coli O157:H7 can survive for about 30 days before reaching the detection limit in soils from Salinas Valley CA and about 20 days in soils from Imperial Valley CA and Yuma AZ. The survival of E. coli O157:H7 in soils was controlled by multiple factors, with the dominant factor being salinity (EC). The interactions between indigenous microbial population and the introduced pathogen was very complex as evidenced by the fact that different bacterial groups displayed distinct effects on the survival of E. coli O157:H7. The results of this research will be used by growers, researchers, FSIS, FDA, and different state agencies regulating leafy green production.

Technical Abstract: Persistence of Escherichia coli O157:H7 in 32 (16 organically managed and 16 conventionally managed) soils from California (CA) and Arizona (AZ) was investigated. Results showed that the longest survival (ttd, time needed to reach detection limit, 100 CFU/g dry soil) of E. coli O157:H7 was observed in the soils from Salinas Valley, CA and in organically managed soils from AZ. Detrended correspondence analysis revealed that the survival profiles in organically managed soils in Yuma, AZ were different from the ones in conventionally managed soils from the same site. Principal component analysis and stepwise regression analysis showed that E. coli O157:H7 survival in soils was negatively correlated with salinity (EC) (P < 0.001), while positively correlated with assimilable organic carbon (AOC) and total nitrogen (TN) (P < 0.01). Pearson correlation analysis revealed that a greater ttd was associated with a larger d (time needed for first decimal reduction in E. coli population). EC was negatively correlated and TN was positively correlated (P < 0.05) with d, suggesting that EC and TN likely have a direct impact on ttd. On the other hand, AOC showed a close correlation with p (the shape parameter) that was not directly related to ttd, indicating that AOC might have an indirect effect in the overall survival of E. coli O157:H7 in soils. Our data showed that AOC and EC significantly affected the survival of E. coli O157:H7 in leafy green producing soils and the development of good agricultural practices (manure/composting/irrigation water source management) in the preharvest environment must be followed to minimize foodborne bacterial contamination on fresh produce.

Last Modified: 9/29/2014
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