Title page for ETD etd-08162009-211103

Type of Document Master's Thesis
Author Pu, Shuaihua
Author's Email Address spu1@lsu.edu
URN etd-08162009-211103
Title Effects of Plant Maturity and Bacterial Inoculum Level on the Surface Contamination and Internalization of Escherichia coli O157:H7 in Growing Spinach
Degree Master of Science (M.S.)
Department Food Science
Advisory Committee
Advisor Name Title
Ge, Beilei Committee Chair
Beaulieu, John C. Committee Member
Prinyawiwatkul, Witoon Committee Member
  • surface contamination
  • internalization
  • Escherichia coli O157:H7
  • inoculum level
  • maturity
  • spinach
Date of Defense 2009-06-02
Availability unrestricted
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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