IAFP 2009 Program Book and Abstract Book - AB155

day and 15°C at night for 2 days; (2) 32°C during the day and 15°C at night for 3 days. Control plants were grown at 23°C during the day and 7°C at night. Roots, leaves and soil samples were collected immediately after receiving the heat stress treatments and assayed for E. coli O157:H7. Results: After enrichment culture, all inoculated soil and rhizosphere samples from inoculated soil were positive for E. coli O157:H7. All leaf surfaces and ground leaves after surface disinfection were E. coli O157:H7-negative. After surface disinfection, all ground roots, except for one, were E. coli O157:H7-negative. Slightly less E. coli O157:H7 populations were detected in soil samples held under heat stress than in those from inoculated control soil. Significance: Heat stress during growth of lettuce under different soil moisture conditions did not cause internalization of E. coli O157:H7 in Romaine or iceberg lettuce plants. P3-19 Surface Water Irrigation Disinfection in Lettuce Production MARA MASSEL, Jose Grazon, Garry Grabow, Chris Gunter and Trevor Phister North Carolina State University, Food, Bioprocessing and Nutrition Sciences, Raleigh, NC, USA Introduction: Irrigation water has been implicated in a number of produce-related foodborne illness outbreaks, most recently with Salmonella Saintpaul on fresh market tomato and pepper. Purpose: In this study, we examine the use of calcium hypochlorite delivered via the PPG Accutab® Chlorination system to treat agricultural surface water used for drip and sprinkler irrigation. Methods: Lettuce beds were prepared using standard methods at the University research farm. Irrigation was applied through either the use of drip tape under black plastic mulch or sprinklers (overhead). In the overhead irrigation portion of the study, drip irrigation was used to apply fertilizers to the developing plants and to eliminate the possibility of confounding results due to fertilizers contacting developing leaves. Treatments included overhead irrigation with and without chlorination and drip irrigation with and without chlorination, for a total of four unique treatment combinations. Each treatment was replicated three times. Fecal coliform levels in the irrigation water and on the leaves were tested with either a ten-tube or three-tube MPN as outlined in the FDA Bacterial Analytical Manual. Free chlorine levels were monitored at the furthest end of the treatment application (either the last drip tape or the furthest sprinkler) and were maintained at a level of 1 to 3 ppm free chlorine. Results: While the fecal coliform levels in the water were low, the levels reached > 1600 MPN/100 mL during the season in the non-chlorinated irrigation water. The levels in both chlorinated systems remained < 1.8 MPN/100mL. Significance: The results suggest that this system is effective in controlling irrigation water contamination. While fecal coliforms where monitored on the leaves, their levels were low, and the only discernible contamination did not correlate to irrigation method or chlorination. These studies will be repeated in the 2009 growing season, using tracer organisms to follow the transfer rates from water to lettuce. P3-20 Effect of Sodium Hypochlorite and High Power Ultrasound on Escherichia coli O157:H7 in Lettuce Homogenate and on Romaine Lettuce NICOLE D. MAKS, Darren Bates, Stephen Grove and Alvin Lee National Center for Food Safety and Technology, Summit-Argo, IL, USA Introduction: The 2006 E. coli O157:H7 outbreak in spinach caused great concern over the safety of leafy greens, and improving product safety became a priority. Sodium hypochlorite is a sanitizer widely used by the fresh produce industry to reduce microbial contamination in produce wash water. The incorporation of a non-thermal process such as high power ultrasound (HPU) during produce washing may be one way to enhance the safety of leafy greens. Purpose: The objective was to determine whether the use of sodium hypochlorite in combination with HPU increases the reduction of E. coli O157:H7 in lettuce homogenate and on the surface of lettuce. Methods: Two strains of E. coli O157:H7 were used separately for the homogenate and inoculated lettuce tests, and experiments were performed in duplicate at 10 and 20°C. E. coli O157:H7 suspended in lettuce homogenate (~8 log) was added at 1:10 (v/v) to 25-200 ppm sodium hypochlorite and was treated with or without HPU for 15, 30, 60 or 120 s and the sanitizer was neutralized. Romaine lettuce pieces (5 cm2) were spot inoculated with 100 µl E. coli O157:H7 (~7 log), dried then immersed in 700 ml sodium hypochlorite (50 to 200 ppm) with or without HPU for 120 s. Results: An additional 0.5 to 1 log reduction with HPU at both 10 and 20°C was observed when E. coli O157:H7 was suspended in lettuce homogenates and treated with 100 ppm sodium hypochlorite for 120 s. Further reductions in E. coli counts were observed at 150 and 200 ppm sanitizer with HPU. Treating inoculated lettuce pieces with 50 ppm sodium hypochlorite at 10°C provided an additional 1.5 log reduction when HPU was used. At 20°C with HPU, an additional reduction (2 log) was seen with 200 ppm sodium hypochlorite. Significance: The results suggest that HPU in combination with an appropriate sanitizer may enhance removal or inactivation of E. coli O157:H7 during washing of romaine lettuce. P3-21 Microbial Contamination of Spinach Placed in Close Proximity of Cattle Feed Yard Operations SUNDEEP YANAMALA, Mindy M. Brashears, Guy H. Loneragan and Markus F. Miller Texas Tech University, Animal and Food Science, Lubbock, TX, USA Introduction: In the fall of 2006, there was a major outbreak of illnesses caused by E. coli O157:H7 linked to spinach. Trace back investigations resulted in identification of the origin of contaminated product, but the mode of contamination was not determined. The place of source of contamination was identified as California, where a great deal of produce is cultivated in close proximity to cattle feed yards. Spinach is exposed to several environmental factors throughout the growing process that can cause contamination. Abstract Book — 155 Poster

IAFP 2009 Program Book and Abstract Book

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