| 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 |
|
| Keywords |
- surface contamination
- internalization
- Escherichia coli O157:H7
- inoculum level
- maturity
- spinach
|
| Date of Defense |
2009-06-02 |
| Availability |
unrestricted |
Abstract
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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| Files |
| Filename |
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56K Modem |
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ISDN (128 Kb) |
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Puthesis.pdf |
736.99 Kb |
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