Transfer of Escherichia
coli O157:H7 from Soil, Water, and Manure Contaminated with Low Numbers of the Pathogen to Lettuce Plants
The sources of contamination of leafy greens remain unclear, but it is evident that contaminated water, soil amendments, and wildlife likely contribute. The objective of the present study was to determine transfer of low numbers of Escherichia coli O157:H7 from soil, manure-amended
soil, and water to growing lettuce plants. Lettuce plants, young (12 days of age) or mature (30 days of age), were grown in soil, manure-amended soil, or irrigated with water containing 101, 102, 103, or 104 CFU E. coli O157:H7 per g or ml.
Harvested plants were processed to determine whether E. coli O157:H7 was associated with the entire plant or within internal locations. Young plants (12 days) were harvested at 1, 10, 20, and 30 days postexposure. No samples were positive for E. coli O157:H7 after direct plating
of serial dilutions. Enrichment of all samples from young plants exposed to contaminated soil, manure-amended soil, and irrigation water demonstrated that approximately 21% (113 of 552) of plants were positive for E. coli O157:H7. Approximately 30% (36 of 120) of the mature plants initially
irrigated with or grown in contaminated soil (including manure-amended soil) for 15 days were positive for E. coli O157:H7. Based on sterilization of surface tissue, E. coli O157:H7 was in protected locations of lettuce tissue. The results suggest that lettuce exposed to, and
grown in the presence of, low numbers of E. coli O157:H7 may become contaminated and thus present a human health risk.
Document Type: Research Article
Department of Food Science, School of Environmental and Biological Sciences, Rutgers, The State University of New Jersey, 65 Dudley Road, New Brunswick, New Jersey 08901-8520, USA
Department of Food Science, School of Environmental and Biological Sciences, Rutgers, The State University of New Jersey, 65 Dudley Road, New Brunswick, New Jersey 08901-8520, USA;, Email: firstname.lastname@example.org
Publication date: November 1, 2009
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