Purpose: The objective of this research was to determine the possible transmission route of E. coli O157:H7 into the phyllo-plane of wheat using contaminated seed, soil, or water and survivability of E. coli on wheat heads.
Methods: A cocktail of five kanamycin-resistant strains of E. coli O157:H7 was used to contaminate the seeds, soil or irrigation water with 6.88 log CFU/g, 6.60 log CFU/g and 6.76 log CFU/ml, respectively. Seedlings were harvested after 9 days post-inoculation. A fourth experiment was conducted in which flowering wheat heads were sprayed with contaminated water (4.19 log CFU/ml) and harvested after 15 days. Approximately one hundred plants per experiment were sown, watered every day, surface sanitized (except in the fourth experiment), enriched with selective media, and analyzed by qPCR detection kits.
Results: Internalization of E. coli into wheat seedlings using contaminated seed, soil, and irrigation water occurred at a rate of 2% (96 samples tested), 5% (100 samples tested) and 10% (100 samples tested), respectively. The wheat head contamination experiment showed the ability of E. coli O157:H7 to survive on the plant for at least 15 days (100% survival, 98 samples tested).
Significance: Even though the internalization rate shown was low in seedlings, this is the first study demonstrating the ability of E. coli O157:H7 to reach the internal tissues of the wheat phyllo-plane. Furthermore, surface contamination and the ability of E. coli O157:H7 to survive long-term on wheat heads should be considered when addressing food safety concerns.