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Escherichia coli O157:H7 is a human pathogen that can cause a wide spectrum of disease symptoms, such as bloody diarrhea, hemorrhagic colitis, and hemolytic uremic syndrome (HUS). Escherichia coli O157:H7 illness are mainly associated with undercooked beef; however, in recent years outbreaks have been linked to fresh produce such as spinach, lettuce, and sprouts. In 2009, flour was implicated as a contamination source in the consumption of raw cookie dough resulting in 77 illness-cases. The objective of this research was to determine the possible route of transmission of E. coli O157:H7 into the phyllo-plane of wheat using contaminated seed, soil or irrigation water. Levels of contamination were 6.88 log CFU/g, 6.60 log CFU/g and 6.76 log CFU/ml of Kanamycin resistant E. coli O157:H7. One hundred plants per treatment were sown in pots trays with 50 g of sterile soil, watered every day with 5 ml of dilution water and harvested after 9 days post-inoculation. In a fourth experiment, flowering wheat heads were spray-inoculated with water containing 4.19 log CFU/ml of E. coli O157:H7 and analyzed for survival after 15 days, close to the harvest period. To detect low levels of internalization, BioTecon q-PCR detections assays were used to determine the presence of E. coli O157:H7 in the wheat plants using a Roche Applied Science LightCycler 2.0.
Results showed that internalization was possible using contaminated seed, soil, and irrigation water in wheat seedlings with an internalization rate of 2%, 5% and 10% respectively. Even though this rate is low, this is the first study to demonstrate the ability of this strain to reach the phyllo-plane in wheat. In the head contamination experiment, all samples tested positive, showing the ability of E. coli O157:H7 to survive on the wheat head phyllo-plane. Although possible this research does not provide evidence for efficient uptake of E. coli O157:H7 into the internal tissue of wheat plants from a contaminated environment. However, surface contamination and the ability of E. coli O157:H7 to survive long-term on the wheat plants is an issue to be considered when addressing food safety issues in products derived from wheat.
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