Understanding the Role of Agricultural Practices in the Potential Colonization and Contamination by Escherichia coli in the Rhizospheres of Fresh Produce
Abstract:To better protect consumers from exposure to produce contaminated with Escherichia coli, the potential transfer of E. coli from manure or irrigation water to plants must be better understood. We used E. coli strains expressing bioluminescence (E. coli O157:H7 lux) or multiantibiotic resistance (E. coli 2+) in this study. These marked strains enabled us to visualize in situ rhizosphere colonization and metabolic activity and to track the occurrence and survival of E. coli in soil, rhizosphere, and phyllosphere. When radish and lettuce seeds were treated with E. coli O157:H7 lux and grown in an agar-based growth system, rapid bacterial colonization of the germinating seedlings and high levels of microbial activity were seen. Introduction of E. coli 2+ to soil via manure or via manure in irrigation water showed that E. coli could establish itself in the lettuce rhizosphere. Regardless of introduction method, 15 days subsequent to its establishment in the rhizosphere, E. coli 2+ was detected on the phyllosphere of lettuce at an average number of 2.5 log CFU/g. When E. coli 2+ was introduced 17 and 32 days postseeding to untreated soil (rather than the plant surface) via irrigation, it was detected at low levels (1.4 log CFU/g) on the lettuce phyllosphere 10 days later. While E. coli 2+ persisted in the bulk and rhizosphere soil throughout the study period (day 41), it was not detected on the external portions of the phyllosphere after 27 days. Overall, we find that E. coli is mobile in the plant system and responds to the rhizosphere like other bacteria.
Document Type: Research Article
Affiliations: 1: Crop and Soil Sciences, 1109 Experiment Street, The University of Georgia, Griffin Campus, Griffin, Georgia 30223, USA 2: Laboratory for Soil Microbiology, College of Agriculture, Lilly Hall of Life Sciences, 915 West State Street, West Lafayette, Indiana 47907, USA 3: Department of Food Science, 754 Agriculture Mall Drive, Purdue University, West Lafayette, Indiana 47907, USA
Publication date: November 1, 2010
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