IAFP 2009 Program Book and Abstract Book - AB41

Significance: The stress encountered in the rhizosphere and intact plant tissue prevents the uptake of E. coli O157:H7 from soils to spinach plant shoot tissue. No differences in the ability of O157:H7 and commensal E. coli to internalize to spinach plants were observed. T5-02 Attachment of Salmonella spp. to Intact and Cut Produce Surfaces JITU PATEL, Katherine Hopkins and Ernie Paroczay USDA-ARS, Beltsville, MD, USA Introduction: Salmonella outbreaks have been associated with the consumption of fresh produce. The produce may be contaminated with Salmonella at any point throughout the food continuum. To develop effective strategies to minimize the risk of foodborne disease caused by this organism, it is essential to examine initial stages of bacterial attachment to various plant tissues. Purpose: The purpose of this study was to evaluate the attachment of Salmonella spp. to different produce surfaces. Methods: Three types of fresh produce (lettuce: romaine and iceburg, cabbage) were used in the study. Two configurations of coupons: 2-cm disk shaped produce coupons (intact surface) and 2 × 0.5-cm strips cut from mid-vein of leaf at the thickest point near the base of produce (cut surface) were used. Coupons/strips (n = 360) were submerged into four individual Salmonella spp. and stored at 10°C for up to 24 h. Samples were removed periodically and analyzed for loosely attached cells (those removed when samples were vortexed for 20 s in PBS/Tween20) and strongly attached cells (those removed when samples were homogenized for 20 s using high speed homogenizer). Results: Attachment to produce surfaces among Salmonella spp. was variable. Attachment of S. Tennessee to produce surfaces was significantly greater than the attachment of S. Negev. Salmonella attachment to cabbage was significantly lower than the attachment to romaine or iceburg lettuce. Most Salmonella were attached to cut surface at levels 0.4-1 log CFU/ml above numbers on intact surface. However, the difference between bacterial attachment to intact and cut surfaces was not significant for lettuce. Populations of loosely attached Salmonella on cabbage and iceburg lettuce surfaces were significantly greater than populations of strongly attached bacterial populations on these produce. Most bacterial attachment occurred during the first hour of exposure to produce surface. Significance: The study shows the preferential attachment of Salmonella to produce surfaces. Further, Salmonella binds rapidly to plant tissues irrespective of the type of produce. Results may aid in understanding the contamination process and in developing effective mitigation strategies. T5-03 Effect of Fresh Produce Crop Residue on the Survival of Escherichia coli O157:H7 in Soil XIANGWU NOU, Patricia Millner, Jitu Patel, Manan Sharma and David Ingram USDA-ARS BARC, EMFSL, Beltsville, MD, USA Introduction: Significant amounts of un-harvested crop residues are incorporated into the soil at the end of the growing seasons on leafy green produce fields. The extent to which these plant remnants contribute to persistence of soil and produce contamination by bacterial pathogens during the subsequent growing season is unclear. Purpose: The purpose was to evaluate the effects of decomposing plant residues on the survival and proliferation of E. coli O157:H7 in soil. Methods: Spinach leaves and soil were inoculated with several E. coli O157:H7 strains and buried in soil with leaves of cabbage, tubers of forage radish, or spinach. Survival and proliferation of inoculated pathogenic strains was measured for 35 days during biomass decomposition using MPN procedures. Results: No significant proliferation of E. coli O157:H7 strains occurred during the 5 week biomass decomposition period. However, E. coli O157H7 survival was significantly affected by type of decaying biomass. When E. coli O157:H7inoculated spinach leaves were exposed to cabbage biomass, the pathogen population declined by 5.0 log after 35 days of decomposition in soil, compared with 3.4, 3.0, and 3.3 log when exposed to biomasses of spinach, radish tubers, or soil without added biomass, respectively. Survival of E. coli O157:H7 inoculated from bovine fecal solids was not significantly affected when different types of crop biomass were tested. Significance: Cabbage and other brassicaceous plants have robust glucosinolate-myrosinase systems. Several glucosinalate hydrolysis products released during decomposition may reduce survival of bacterial pathogens under certain conditions (soil biofumigation). Data from this study suggests that biofumigation in conjunction with Brassica plant rotation could be an effective means of mitigating field contamination by bacterial pathogens in leafy green production systems. T5-04 Transfer of Escherichia coli O157:H7 from Equipment Surfaces to Iceberg and Romaine Lettuce during DSC Simulated Commercial Processing ANNEMARIE L. BUCHHOLZ, Gordon R. Davidson, Bradley P Marks, Ewen C. Todd and Elliot T. Ryser . Michigan State University, Food Science and Human Nutrition, East Lansing, MI, USA Introduction: Cross-contamination/multi-directional transfer of Escherichia coli O157:H7 during commercial shredding, conveying, fluming and drying of fresh-cut leafy greens has become a major public health concern, particularly because post-processing kill steps are currently not implemented in the industry. Purpose: The goal of this study was to quantify E. coli O157:H7 transfer from product-inoculated equipment surfaces to uninoculated lettuce during commercial processing. Methods: Three to five batches of locally purchased retail iceberg and romaine lettuce (136 kg/batch) were cored, after which 22.7 kg of product was dip-inoculated to contain ~106, 104 or 102 CFU/g of a 4-strain avirulent, gfp-labeled, ampicillin-resistant E. coli O157:H7 cocktail. Thereafter, 22.7 kg of each uninoculated product was processed, using a Abstract Book — 41 Technical

IAFP 2009 Program Book and Abstract Book

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