IAFP 2009 Program Book and Abstract Book - AB154

Significance: These results indicate that a typical fermentation time of two or more weeks may be sufficient to assure the destruction of pathogenic E. coli strains in fermentation brines, independent of active bacterial competition. P3-16 Pre-harvest Internalization of Escherichia coli O157:H7 into Lettuce Leaves as Impacted by the Presence of Insects MARILYN C. ERICKSON, Jean Liao, Alison Payton, David Riley, Cathy Webb, Lindsey McGhin, Sophia Tison, Michael Doyle, Larry Beuchat, Guodong Zhang and Li Ma University of Georgia, Center for Food Safety, Griffin, GA, USA Introduction: Environmental pests serve as reservoirs and vectors of zoonotic pathogens; however, it is unknown whether insect pests, through their feeding activities, could also redistribute the pathogen on contaminated leaves to internal sites of plant tissue. Purpose: To differentiate the degree of tissue internalization of E. coli O157:H7 applied at various concentrations to lettuce leaves (abaxial or adaxial side) and subjected to mechanical abrasion; and to ascertain whether insects that commonly infest lettuce could stimulate internalization of surface-contaminated pathogens. Methods: An inoculum mixture of gfp-labeled E. coli O157:H7 (5 isolates) at 106 to 108 CFU/ml was applied (25 µl) as a fine mist or as fine drops to either the abaxial or adaxial surface of lettuce leaves and analyzed after potted plants had benn held for 48 h within an environmental growth chamber. Immediately after drop inoculation, a rounded glass rod was rubbed very gently over the surface. In a separate experiment, leaves were exposed for 24 h to one of 4 insect types (5 cabbage loopers, 10 aphids, 10 thrips, or 15 whiteflies) either prior to or following leaf inoculation. For each trial, a portion of inoculated leaves were analyzed for total populations of E. coli O157:H7 while the other portion received a surface disinfection treatment (ethanol/HgCl2) prior to grinding the tissue and analyzing for internalized pathogen populations. Results: No internalization of E. coli O157:H7 occurred when leaves were exposed to a 106 CFU/ml spray. Pathogen internalization did occur when exposed to a 108 CFU/ml spray, and higher incidences were noted for contaminated abaxial (underside) compared to adaxial (topside) leaves and leaves subjected to mechanical abrasion. Exposure of surfacecontaminated leaves to insects reduced the number of leaves having internalized E. coli O157:H7. Significance: Understanding the conditions that contribute to pathogen internalization and survival within leafy greens will be valuable in developing pre-harvest management practices for producing a safe product. P3-17 Internalization of Enteric Viruses in Spinach and Green Onions KIRSTEN A. HIRNEISEN, Haiquang Chen, Randy W. Worobo, Karl R. Matthews and Kalmia E. Kniel University of Delaware, Dept. of Animal and Food Sciences, Newark, DE, USA Introduction: There have been several outbreaks of hepatitis A virus (HAV) linked to the consumption of fresh produce, including strawberries, lettuce and green onions. Sources of viral contamination of produce remains unclear; however, contaminated water, soil, flooding fields and wildlife are likely to contribute. HAV has been shown to be internalized in hydroponically grown green onions. Purpose: This study addressed pre-harvest routes of enteric virus introduction into fresh produce. Virus survival in soil and internalization into growing spinach and green onion plants through contaminated soil and water were investigated. Methods: Spinach and green onion seeds were planted and grown in the University of Delaware greenhouse. Ten days post planting, plants were transferred to growing pots with soil or water contaminated with 2 × 107 log TCID50/g HAV. Days 5, 10 and 20 post-inoculation plant samples were collected, washed with Virkon to remove external viruses present and homogenized in Na2HPO4 (pH 9.5) to release internal virus particles. Both plant and soil samples were analyzed by TCID50 and qPCR. Results: Internalized HAV was detected by qPCR on day 5 post-inoculation in one spinach plant contaminated through inoculated soil. This spinach plant contained 2.43 logs PCR units/mL of HAV internally; however, HAV was not detected in this spinach plant through TCID50 analysis. HAV was undetectable in all other plant and soil samples between days 5 and 20, which could be due to adsorption of the virus particles to the soil. Viral recovery and survival in soil will be further investigated. Significance: In spinach and green onions grown under natural conditions and exposed to a single inoculation of contaminated water, HAV did not internalize into plants according to results with current evaluation techniques. Contaminated soil produced HAV internalization in one plant; however, after 5 days post inoculation, HAV was not detectable. P3-18 Effect of Heat and Drought Stress during Growth of Lettuce (Lactuca sativa L.) on Internalization of Escherichia coli O157:H7 GUODONG ZHANG, Li Ma, Larry R. Beuchat, Marilyn C. Erickson, Vanessa H. Phelan and Michael P Doyle . University of Georgia, Center for Food Safety, Griffin, GA, USA Introduction: Outbreaks of E. coli O157:H7 associated with lettuce and spinach have raised questions regarding the potential for internalization of E. coli O157:H7 in vegetables, especially when grown under stressful conditions such as high temperature, drought, or waterlogging. Purpose: The objective of this study was to determine if heat stress during growth of lettuce under different water conditions in soil caused internalization of E. coli O157:H7 in leaves or roots. Methods: Iceberg and Romaine lettuce were grown in sandy soil in an environmental chamber at 23°C during the day and 7°C at night. Thirty days after transplantation, potting soil with lettuce was inoculated with a 5-strain mixture of E. coli O157:H7 at 104 and 106 CFU/g soil. The lettuce plants were exposed to two temperature regimes, i.e., (1) 36°C during the 154 — Abstract Book Poster

IAFP 2009 Program Book and Abstract Book

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