4. AOACRIMicroMethods-2018Awards

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B ird et al .: J ournal of AOAC I nternational V ol . 96, N o . 4, 2013  813

The MPNs obtained for this matrix, with 95% confidence intervals, were 1.10 CFU/test portion (0.49, 2.46) for the low inoculum level and 4.38 CFU/test portion (1.71, 11.20) for the high inoculum level.

the SPR. The test value is calculated by the instrument and is equal to the difference between the background reading and the final reading. The calculation appears on the result sheet. A negative result has a test value less than the threshold (0.25) and indicates that the sample does not contain Salmonella spp. or contains Salmonella spp. at a concentration below the detection limit. A positive result has a test value equal to or greater than the threshold (≥0.25) and indicates that the sample may be contaminated with Salmonella spp. If the background reading is above a predetermined cutoff, then the result is reported as invalid (Table 2012.01D ). G. Confirmation All positive VIDAS SPT results must be culturally confirmed. Confirmation should be performed using the non- heated enrichment broth stored between 2 and 8°C, and should be initiated within 72 h after the end of incubation at 42 ± 1°C. Presumptive positive results may be confirmed by isolating on selective agar plates such as IBISA or ASAP, or on the appropriate reference method selective agar plates. Typical or suspect colonies from each plate are confirmed as described in AOAC Official Method 967.27 . As an alternative to the conventional tube system for Salmonella , any AOAC-approved commercial biochemical kits may be used for presumptive generic identification of foodborne Salmonella as described in AOAC Official Methods 978.24 , 989.12 , 991.13 , and 2011.17 . In this collaborative study, the VIDAS SPT method was compared to the to the USDA/FSIS-MLG reference method for one food product, raw ground beef, at two different test portion sizes, 25 and 375 g. A total of 15 laboratories throughout the United States participated in this study, with 14 submitting data for each matrix, as presented in Table 1. Each laboratory analyzed 36 test portions for each method: 12 inoculated with a high level of Salmonella , 12 inoculated with a low level, and 12 uninoculated controls. For each test portion size, the actual level of Salmonella was determined by MPN determination on the day of initiation of analysis. Individual laboratory and sample results are presented in Tables 2–5. Tables  2013.01A  and  B summarize the interlaboratory results for all foods tested, including POD statistical analysis (6). Detailed results for each laboratory are presented in Tables A–F of the Appendix. Raw ground beef test portions were inoculated at a low and high level, and analyzed (Tables 2 and 3) for the detection of Salmonella spp. Uninoculated controls were included in each analysis. Fourteen laboratories participated in the analysis of this matrix, and the results of 12 were included in the statistical analysis. Laboratory 8 reported that it was unable to confirm samples via serological testing and indicated that it did not conduct the alternative confirmation of the VIDAS SPT samples. Therefore, its results were not included in statistical analysis. Laboratory 12 produced a low-level presumptive positive result for one of its uninoculated control test portions, which could not be confirmed positive by the traditional reference method. Therefore, its results were not included in the statistical analysis. 03/10/2019 Results of Collaborative Study Raw Ground Beef (25 g Test Portions)

Traditional Confirmation with Xylose-Lysine-Tergitol 4 (XLT4) and Brilliant Green Sulfa (BGS)

For the high inoculum level, all of the 144 test portions were reported positive by the VIDAS SPT method, with all portions confirming positive. For the low inoculum level, all 144 test portions were also reported as positive by the VIDAS SPT method, with 143 confirming positive, indicating one false unconfirmed positive result (Laboratory 6). For the uninoculated controls, none of the 144 samples produced a presumptive positive result by the VIDAS SPT method, and all samples confirmed negative. For test portions analyzed by the USDA/ FSIS-MLG method, 138 out of 144 high and 84 out of 144 low inoculum test portions confirmed positive. For the uninoculated controls, none of the 144 test portions confirmed positive. For the low-level inoculum, a dLPOD C value of 0.41 (+0.32, +0.49) was obtained between the USDA/FSIS-MLG method and the VIDAS SPT method. The confidence intervals obtained for dLPOD C indicated a statistically significant difference between the two methods. However, the VIDAS SPT method detected more positive samples than the USDA/FSIS-MLG reference method, indicating a higher level of sensitivity than the reference method. A dLPOD CP of 0.01 (–0.02, +0.04) was obtained between presumptive and confirmed VIDAS SPT results for both confirmation procedures. The confidence intervals obtained for dLPOD CP indicated no significant difference between the presumptive and confirmed results. For the high-level inoculum, a dLPOD C value of 0.04 (+0.01, +0.09) was obtained between the USDA/FSIS-MLG method and the VIDAS SPT method. The confidence intervals obtained for dLPOD C indicated a statistically significant difference between the two methods. However, the VIDAS SPT method detected more positive samples than the USDA/FSIS-MLG reference method, indicating a higher level of sensitivity than the reference method. A dLPOD CP of 0.00 (–0.03, +0.03) was obtained between presumptive and confirmed VIDAS SPT results. The confidence intervals obtained for dLPOD CP indicated no significant difference between the presumptive and confirmed results. Results of the POD statistical analysis are presented in Table 2013.01A , and in appended Table A and Figure 1A and B. For the high inoculum level, all 144 test portions were reported as positive by the VIDAS SPT method, with all confirming positive. For the low inoculum level, all 144 test portions were also reported as positive by the VIDAS SPT method, with 143 confirming positive. For the uninoculated controls, none of the 144 samples produced a presumptive positive result by the VIDAS SPT method with all samples confirming negative. For test portions analyzed by the USDA/FSIS-MLG method, 138 of the 144 high inoculum test portions and 84 out of 144 low inoculum test portions confirmed positive. For the uninoculated controls, none of the 144 test portions confirmed positive. For the low-level inoculum, a dLPOD C value of 0.41 (+0.32, Traditional Confirmation with IBISA and ASAP