4. AOACRIMicroMethods-2018Awards

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B ird et al .: J ournal of AOAC I nternational V ol . 96, N o . 4, 2013  809

nonmotile Salmonella. The assay is performed in the automated VIDAS instrument. TheVIDAS SPT assay uses a primary enrichment (prewarmed to 42±1°C for 375 g samples), along with a proprietary supplement (SPT supplement). After 18–24 h of enrichment (22–26 h for 375 g samples), Salmonella detection is performed by the VIDAS SPT test. The new enrichment method eliminates the need for secondary enrichments [Tetrathionate Hanja (TTH), Rappaport-Vasilliadis (RV), and SX2 broths]. Negative results and presumptive positive results are available the day after enrichment. Prior to the collaborative study, the VIDAS SPT method was validated according to AOAC guidelines for harmonized Performance Tested Method SM (PTM) studies (2). The purpose of this study was to demonstrate that the VIDAS SPT method could detect Salmonella in a variety of foods and environmental surfaces as claimed by the manufacturer. For the VIDAS SPT PTM evaluation, 17 matrixes were tested using buffered peptone water (BPW) plus Salmonella supplement enrichment protocol: raw ground beef (25 and 375 g), processed American cheese (25 g), deli roast beef (25 g), liquid egg (25 g), peanut butter (25 g), vanilla ice cream (25 g), cooked shrimp (25 g), raw cod (25 g), bagged lettuce (25 and 375 g), dark chocolate (375 g), powdered eggs (25 g), instant nonfat dry milk (25 and 375 g), ground black pepper (25 g), dry dog food (375 g), and stainless steel, plastic, and ceramic environmental surfaces. In a matrix extension evaluation conducted in February 2012, three additional foods were evaluated using BPW plus Salmonella supplement enrichment protocol: raw ground turkey (375 g), almonds (375 g), and chicken carcass rinsates (30 mL). One matrix, raw ground beef (375 g), was evaluated using a different enrichment protocol, BPW plus vancomycin, to allow for a single enrichment when the VIDAS SPT and E. coli Phage Technology (bioMérieux) assays were used. All other PTM parameters (inclusivity, exclusivity, ruggedness, stability, and lot-to-lot variability) tested in the PTM studies satisfied the performance requirements for PTM approval. The method was awarded PTM certification No. 071101 on July 15, 2011 with a matrix extension approval on March 23, 2012. This collaborative study compared the VIDAS SPT method to the U.S. Department of Agriculture/Food Safety and Inspection Service- Microbiology Laboratory Guidebook (USDA/FSIS-MLG) 4.05 (2011) Isolation and Identification of Salmonella from Meat, Poultry, Pasteurized Egg and Catfish Products method (3) for raw ground beef at two test portion sizes, 25 and 375 g. Study Design For this collaborative study, one matrix, raw ground beef (80% lean), was analyzed using two different test portion sizes, 25 and 375 g. The raw ground beef was obtained from local retailersandscreenedfortheabsenceof Salmonella bytheUSDA/ FSIS-MLG reference method prior to analysis. The screening indicated an absence of indigenous Salmonella . For analysis of the 25 g test portions, the raw ground beef was artificially contaminated with Salmonella Enteritidis ATCC 13076 and with Salmonella Montevideo ATCC 8387 for the analysis of the 03/10/2019 Collaborative Study

375 g test portions. There were two inoculation levels: a high inoculation level of approximately 2–5 CFU/test portion and a low inoculation level of approximately 0.2–2 CFU/test portion. A set of uninoculated control test portions were also included for each matrix at 0 CFU/test portion. Twelve replicate samples from each of the three inoculation levels of product were analyzed. Two sets of samples (72 total) were sent to each laboratory for analysis by VIDAS SPT and the USDA/FSIS-MLG reference method due to different sample enrichments for each method. For both test portion sizes, collaborators were sent an additional 30 g test portion and instructed to conduct a total aerobic plate count on the day samples were received in order to determine the total aerobic microbial load in the matrix. A detailed collaborative study packet outlining all necessary information related to the study, including media preparation, method-specific test portion preparation, and documentation of results, was sent to each collaborating laboratory before initiation of the study. The Salmonella cultures used in this evaluation were propagated in 10 mL Brain Heart Infusion broth from a frozen stock culture held at –70°C at Q Laboratories, Inc. The broth was incubated for 18–24 h at 35±1°C. Appropriate dilutions were prepared based on previously established growth curves for both low and high inoculation levels, resulting in fractional positive outcomes for at least one level. For both test portion sizes, a bulk lot of the raw ground beef was inoculated with a liquid inoculum and mixed thoroughly by hand-kneading to ensure even distribution of microorganisms. The raw ground beef was inoculated on the day of shipment so that all test portions would have been held for 96 h by the day testing was initiated. For the analysis of the 25 g test portions, the bulk lot of test material was divided into 30 g portions for shipment to the collaborators. For the analysis of the 375 g test portions, 25 g of inoculated test product was mixed with 350 g of uninoculated test product for shipment to the collaborators for analysis by the VIDAS SPT method. Collaborators received 30 g portions for analysis by the USDA/FSIS-MLG method. To determine the level of Salmonella spp. in the raw ground beef, a five- tube MPN was conducted on the day of initiation of analysis. From both the high and low inoculated batches of raw ground beef, five 100 g test portions, five 25 g test portions, and five 10 g test portions were analyzed using a 1:10 dilution with BPW. The most probable number (MPN) and 95% confidence intervals were calculated from the high, medium, and low levels using the AOAC MPN Calculator (www.lcftld.com/customer/ LCFMPNCalculator.exe; 4). Confirmation of the samples was conducted according to the USDA/FSIS-MLG 4.05 reference method. Preparation of Inocula and Test Portions

Test Portion Distribution

All samples were labeled with a randomized, blind-coded, three-digit number affixed to the sample container. Test portions were shipped on a Thursday via overnight delivery according to the Category B Dangerous Goods shipment regulations set forth by the International Air Transport Association. Upon receipt, samples were held by the collaborating laboratory at refrigeration