IAFP 2009 Program Book and Abstract Book - AB156

Purpose: The objective of this study was to determine if exposure to feed yard dust can cause an increase in the total number of indicator organisms (generic E. coli) in spinach plants. Methods: Spinach bundles were obtained from local grocery store and tested for background microflora. Exposed bundles were set up in an upright position at three locations (0, 20 and 50 yards) from the loading area in the direction of wind. Similarly, a second set of bundles were set under plastic covering at each location, right beside the exposed ones, to serve as a control. Sampling was conducted at 6, 12 and 24 h and total numbers of generic E. coli were determined by use of petrifilm, according to manufacturer’s recommendations, as an indicator of pathogen contamination. A total of four replications were conducted. Results: There was a significant increase in generic E. coli numbers from 0 logs at 0 hours to 1.90, 2.47 and 2.49 logs over 6, 12 and 24 h of exposure, respectively, at 0 yard location. There was a significant increase from 0 logs at 0 hours to 1.85, 2.04 and 2.48 logs over 6, 12 and 24 hours of exposure, respectively, at the 20 yard location. There was a significant increase from 0 logs at 0 hours to 1.71, 2.28 and 2.29 logs over 6, 12 and 24 hours of exposure, respectively, at the 50 yard location. None of the control samples had any generic E. coli numbers throughout the sampling. Significance: Data indicate that the cattle feed yard may potentially contaminate vegetable crops through dust if the crops are in close proximity. It is important to determine pathogen carriage in the dust and the potential for the dust to cause actual pathogen contamination. P3-22 Quantification of Escherichia coli O157:H7 Transfer to Equipment during Commercial Production of Fresh-cut DSC Leafy Greens ANNEMARIE L. BUCHHOLZ, Gordon R. Davidson, Danilo T. Campos, Bradley P Marks, Ewen C. Todd and Elliot T. Ryser . Michigan State University, Food Science and Human Nutrition, East Lansing, MI, USA Introduction: Recent Escherichia coli O157:H7 outbreaks associated with fresh-cut leafy greens have been traditionally traced to field contamination. However, considerable post-harvest cross-contamination can also occur during shredding, conveying, fluming and dewatering, with a current emphasis on recontamination from wash water. Purpose: This study quantified E. coli O157:H7 transfer from dip-inoculated leafy greens to equipment surfaces during simulated commercial processing. Methods: Three to five retail batches (22.7 kg) of baby spinach, iceberg lettuce and romaine lettuce were dip-inoculated to contain a 4-strain cocktail of avirulent, gfp-labeled, ampicillin-resistant E. coli O157:H7 at 106, 104 and 102 CFU/g, drained for one hour and processed using a commercial shredder (model TRS 2500 Urschel TranSlicer), step conveyor, 3.3-m flume tank equipped with two overhead spray jets, shaker table and centrifugal dryer (22.7 kg capacity). During processing, product (25 g) and water (40 ml) samples were collected from the step conveyer, flume tank, shaker table and/or dewatering centrifuge. After processing, 100 cm2 product contact surface samples (n = 50) were collected from the shredder, conveyer, flume tank, shaker table and centrifuge, using Kimwipes®. Sample homogenates in phosphate or neutralizing buffer were plated on trypticase soy agar containing 0.6% yeast extract and 100 ppm ampicillin with or without prior 0.45 µm membrane filtration to quantify gfp-labeled E. coli O157:H7 under UV light. Results: During leafy green processing, 83 to97% of the E. coli O157:H7 inoculum was transferred to the wash water. After processing, E. coli O157:H7 populations were highest on the shredder (5.12 log CFU/g) and conveyor (5.26 log CFU/g) (P < 0.05), followed by the flume tank (3.85 log CFU/g) and shaker table (3.71 log CFU/g), with 30% of the remaining product inoculum lost during centrifugal drying. Significance: This is the first report to quantitatively define both the role and importance of E. coli O157:H7 transfer from product to equipment surfaces during production of fresh-cut leafy greens. A dimensionless predictive model developed using a multi-modal process involving six transfer scenarios (pairwise transfers between product, water, and equipment) will be parameterized as additional data are generated. These findings will ultimately be invaluable in refining current microbial risk assessments being developed for fresh-cut produce. P3-23 Use of the Systems Approach to Determine the Fate of Escherichia coli O157:H7 on Fresh and Fresh-cut Iceberg Lettuce and Spinach MARK A. HARRISON, William L. Kerr, William C. Hurst, Ruth A. Morrow and Helga J. Doering University of Georgia, Athens, GA, USA Introduction: Ideally when evaluating the fate of a pathogen on food the entire processing and handling practice would be studied as a system. Previous studies on contaminated produce have typically focused only on portions of the system. The systems approach allows individual components to be studied in order to see interactions rather than isolated situations. Purpose: The systems approach was used to determine the fate of E. coli O157:H7 in the presence of normal background microorganisms on iceberg lettuce and spinach under conditions that mimic actual practices between production and retail sale. Methods: Lettuce and spinach inoculated with E. coli O157:H7 were processed and handled in ways that might occur in commercial situations (including variations in holding times before and after product cooling, transportation conditions and temperatures, wash treatments, and product storage temperatures and times). Aerobic mesophilic and psychrotrophic bacteria, coliforms, yeasts and molds, lactic acid bacteria and E. coli O157:H7 populations were enumerated after each processing and handling step. Factorial ANOVA was used to predict the response variable with a combination of independent categorical variables and to test hypotheses about the means. Results: Field temperature, time before cooling, and wash treatment significantly affected E. coli O157:H7 populations on both products. On greens packaged and stored at 4°C, E. coli O157:H7 contamination was detected, although populations decreased in many cases by at least 1.5 logs. 156 — Abstract Book Poster

IAFP 2009 Program Book and Abstract Book

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