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Title: Internalization of E. coli O157:H7 in spinach cultivated in soil and hydroponic media

Author
item Sharma, Manan
item Ingram, David
item Patel, Jitu
item Millner, Patricia
item HULL, ANNE
item DONNENBERG, MICHAEL
item WANG, XIAOLIN

Submitted to: International Association for Food Protection Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 3/10/2009
Publication Date: 7/13/2009
Citation: Sharma, M., Ingram, D.T., Patel, J.R., Millner, P.D., Hull, A., Donnenberg, M., Wang, X. 2009. Internalization of E. coli O157:H7 in spinach cultivated in soil and hydroponic media [abstract]. International Association for Food Protection Program Book. p. 40.

Interpretive Summary:

Technical Abstract: Introduction: Internalization of E. coli O157:H7 into spinach plants through root uptake is a potential route of contamination. Previous studies that have investigated uptake of E. coli O157:H7 into leafy greens have expressed green fluorescent protein (gfp) from a plasmid, possibly limiting detection of stressed cells in internal plant tissues. Purpose: The objective of this study was to develop strains of E. coli that contain a chromosomal insert of the gfp gene, and assess the uptake of these strains into spinach plants. Methods: A Tn7-based plasmid vector was used to insert gfpmut2 into the attTn7 site in the E. coli chromosome. Three gfp-labeled E. coli inocula, O157:H7 strains 4407 and 5279 (Inoculum 1), O157:H7 strain 86-24h11 (Inoculum 2), and HS (Inoculum 3), were cultivated in fecal slurries and applied at ca. 3 log CFU/g or 7 log CFU/g to pasteurized soils or to hydroponic media in which baby spinach was planted. Results: No E. coli inocula were recovered by spiral plating from surface-sanitized internal tissues of spinach plants on d 0, 7, 14, 21, and 28 (<1.7 CFU/shoot or root). Inoculum 1 survived at significantly (P<0.05) higher populations than Inoculum 3 after 14, 21 and 28 d in soil. Inoculum 2 applied to hydroponic medium at a ca. 7 log CFU/ml were recovered from the shoots of spinach plants after 14 (3.73 log CFU/shoot) and 21 days (4.35 log CFU/shoot). Fluorescent E. coli cells were primarily visualized in root tissues by microscopy in plants grown in soils, but were not recovered by spiral plating. Significance: The stress encountered in the rhizosphere and intact plant tissue prevents the uptake of E. coli O157:H7 from soils to spinach plant shoot tissue. No differences in the ability of O157:H7 and commensal E. coli to internalize to spinach plants were observed.