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.