A Novel Approach To Investigate the Uptake and Internalization of Escherichia coli O157:H7 in Spinach Cultivated in Soil and Hydroponic Medium

What is it about?

Uptake of E. coli O157:H7 through root tissues of leafy green commodities is a potential route of contamination. Several fluorescent strains of E. coli were modified in a simple and unique manner to carry the green fluorescent protein on the chromosome. E. coli cells were then inoculated at low and high populations into pasteurized soils or into hydroponic media in which baby spinach plants were cultivated. No bacterial populations were recovered from the surface-sterilized internal tissues of spinach plants on day 0, 7, 14, 21, or 28 when plants were grown in soils. When plants were grown hydroponically in the presence of high populations of E. coli, internalized cells of E. coli O157:H7 were recovered consistently on day 14 and day 21. Produce outbreak strains of E. coli O157:H7 survived at higher populations in soils than a commensal strain of E. coli HS. Fluorescent microscopy revealed that E. coli cells are mainly associated with root tissue. The physiological stressed placed on E. coli in inoculated soils and the barriers that intact plant tissue present limit the uptake and internalization of E. coli O157:H7 from soils to spinach plants.

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