4. AOACRIMicroMethods-2018Awards

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C rowley et al .: J ournal of AOAC I nternational V ol . 97, N o . 2, 2014  441

For the analysis of 25 g test portions by the VIDAS LPT method, three false positives were obtained. The test results produced by three false-positive test portions (average test value of 0.34) were much lower than the test values observed with true positives (average value >2.00). By the time the coordinating laboratory received the results, the primary enrichments for these samples had been discarded so no subsequent analysis on the VIDAS LPT was possible. However, the agar plates for these test portions were shipped to the coordinating laboratory for further analysis. Up to 20 different colonies were picked for morphological and biochemical analysis using VITEK 2 GP and no Listeria colonies were identified. Additionally, the entire lawn of growth from each agar plate was swabbed and enriched in separate LPT broth tubes and incubated for 26–30 h at 30 ± 1°C. An aliquot from each tube was analyzed by the VIDAS LPT assay and negative results for Listeria spp. were obtained. Results of this investigation lead the study directors to believe that the false positives were the result of contamination during the analysis of the samples. For the analysis of both the 25 and 125 g test portions, Laboratory 11 detected the presence of multiple species of Listeria . An investigation into the results indicated that colonies picked for confirmation did not meet the characteristics of Listeria spp. (i.e., colonies produced Gram-negative stain reactions, non-motile, negative catalase, or produced hemolysis reactions not typically observed with Listeria spp.). The results of these tests should have precluded analysis using the API strips, which lead to an inaccurate identification. Due to the fact that final results reported were inconsistent with biochemical results, data produced by Laboratory 11 were removed from the statistical analysis of both the 25 and 125 g test portions. Typical growth of Listeria spp. colonies from ALOA was easy to identify and the ALOA plates produced less background ground from the matrix than the OXA plates for both test portions sizes analyzed. Positive comments were received from collaborators about the ease of use associated with the ALOA plates. Using the POD statistical model, no significant difference in the number of positive results obtained between the two methods being compared was observed at both the low- and high-inoculum levels for both the 25 and 125 g test portions. No significant difference was observed between presumptive and confirmed results for the candidate method. The VIDAS UP Listeria (LPT) method with the optional ALOA agar confirmation method was adopted as Official First Action status for the detection of Listeria in a variety of foods and environmental surfaces including deli ham (25 and 125 g), pepperoni (25 g), beef hot dogs (25 g), chicken nuggets (25 g), chicken liver pâté (25 g), ground beef (125 g), deli turkey (125 g), cooked shrimp (25 g), smoked salmon (25 g), whole cantaloupe melon, bagged mixed salad (25 g), peanut butter (25 g), black pepper (25 g), vanilla ice cream (25 g), queso fresco (25 and 125 g), stainless steel, plastic, ceramic, and concrete environmental surfaces. Conclusions

Acknowledgments

We would like to extend a sincere thank you to the following collaborators for their dedicated participation in this study: John Mills and Pat Rule, bioMérieux Industry (Hazelwood, MO) Ben Howard, Neil Rogman, and Jacob Cannon, Certified Laboratories (Bollingbrook, IL) Barbara Paul, Marianna Sala-Rhatigan, and Susan Joseph, U.S. Food and Drug Administration, Northeast Regional Laboratory (Jamaica, NY) Nikki Palen, Amber Stegmann, and Bryan Perry, EMS Laboratories (St. Louis, MO) Rachel Hiles and Tenesha Stubblefield, Silliker Laboratories (Omaha, NE) Nigel Nagassar, Sylvanus Owusu, and Jacqueline Zimmerman, Silliker Laboratories (Minnetoka, MN) Jerry Lynn Pickett, Aaron Bollenbacher, Keith Wiggins, and Lori Cesanas, Tyson WBAAnalytical (Springdale, AR) Bharath Brahmanda, Food Safety Net Services (San Antonio, TX) Andrew Capps, Grisel Rosario, Dawn Davis, Lindsey Parker, Christine Said, and Jianfeng Li, North Carolina Department of Agriculture and CS: Food and Drug Protection Division (Raleigh, NC) Keith Klemms, Bill May, Becky Hand, and Rose Burkhart, Sherry Laboratories (Warsaw, IN) Hesham Elgaali, Indiana State Department of Health, Food and Dairy Microbiology Division (Indianapolis, IN) Jennifer Jolly, Covance Laboratories (Battle Creek, MI) Sandy Moore, Dustin Ebbing, Maggie Michels, Amanda Kehres, and Joe Hirsch, John Morrell (Springdale, OH)  (1) Hitchins, A.D., & Jinneman, K. (2013) Bacteriological Analytical Manual , U.S. Food and Drug Administration, Washington, DC, Chapter 10. http://www.fda.gov/Food/ FoodScienceResearch/LaboratoryMethods/ucm071400.htm.  (2) Chen, Y. (2012) in Bad Bug Book: Handbook of Foodborne Pathogenic Microorganisms and Natural Toxins , Listeria monocytogenes species, 2nd Ed., U.S. Food and Drug Administration, Washington, DC  (3) Centers for Disease Control and Prevention, http://www.cdc. gov/listeria/ (accessed May 2013)  (4) FoodSafety.Gov, http://www.foodsafety.gov/poisoning/causes/ bacteriaviruses/listeria/ (accessed May 2013)  (5)  Official Methods of Analysis (2012) 19th Ed., Appendix J: AOAC INTERNATIONAL Methods Committee Guidelines for Validation of Microbiological Methods for Food and Environmental Surfaces AOAC INTERNATIONAL, Gaithersburg, MD, http://www.eoma.aoac.org/app_j.pdf (accessed March 2013)  (6) Twedt, R.M., Hitchins, A.D., & Prentice, G.A. (1994) J. AOAC Int. 77 , 395–402  (7) Least Cost Formulations, Ltd, MPN Calculator - Version 1.6, http://www.lcfltd.com/customer/LCFMPNCalculator.exe (accessed May 2013)  (8) Least Cost Formulations, Ltd, AOAC Binary Data Interlaboratory Workbook, http://lcfltd.com/aoac/aoac- binary-v2-2.xls (accessed May 2013)  (9) Wehling, P., LaBudde, R., Brunelle, S., & Nelson, M. (2011) J. AOAC Int. 94 , 335–347 References

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