Master of Science (MS)
School of Nutrition and Food Sciences
The incidence of foodborne outbreaks linked to fresh produce has increased in the United States. Particularly noteworthy was the 2006 Escherichia coli O157:H7 outbreak associated with pre-packaged baby spinach. Factors affecting the contamination of spinach leaves with E. coli O157:H7 are not yet well understood. This study aimed to determine whether E. coli O157:H7 would be present in the aerial leaf tissue of a growing spinach plant when introduced at various plant maturities and different inoculum levels in the growth media in a greenhouse setting. Spinach seeds of a standard commercial variety were sown individually in 8-inch pots, watered daily and fertilized weekly after germination. Two levels (103 and 107 CFU) of an E. coli O157:H7 green fluorescent protein (GFP)-expressing strain were introduced into the plant growth media on a weekly basis after germination. Inoculated spinach plants were examined weekly for the presence of E. coli O157:H7 on leaves and in surrounding growth media. Among 120 spinach plant samples examined for internal leaf contamination, only one yielded positive result. Surface leaf contamination occurred occasionally and clustered between 4 to 5 weeks of age, but not among leaves younger than 3 weeks of age. Additionally, when inoculated at 107 CFU level, the E. coli O157:H7 GFP strain survived the entire cultivation period although with gradually reduced levels. The experiments demonstrated that internalization of E. coli O157:H7 of growing spinach plant leaves under greenhouse conditions was a rare event, but surface contamination did occur, primarily when the plants reached 3 weeks of age. The study provided important data to further assess the association between spinach age and potential contamination of E. coli O157:H7.
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Pu, Shuaihua, "Effects of plant maturity and bacterial inoculum level on the surface contamination and internalization of Escherichia coli O157:H7 in growing spinach" (2009). LSU Master's Theses. 4057.