AOAC-RI ERP Book Micro Jan 19 2017

the candidate method’s “confirmation stage” (confirmed) results (POD CC ) at each level of inoculation in order to attain a difference in POD for the two stages (dPOD CP ) at each level of inoculation. A 95% confidence interval was also calculated for each dPOD CP value that was calculated, and was used to determine whether the “screening stage” results is significantly different from the “confirmation stage” results for each level of inoculation. According to the methodology, if the 95% confidence interval of a dPOD CP value does not contain zero, then the difference between the POD CP and the POD CC of the candidate method at that level of inoculation is statistically significant at the 5% level. In addition to these analyses, the rate of true positives (samples with a “screening stage” positive result and “confirmation stage” positive result), the rate of true negatives (samples with a “screening stage” negative result and “confirmation stage” negative result), the rate of false positives (samples with a “screening stage” positive result and “confirmation stage” negative result), and the rate of false negatives (samples with a “screening stage” negative result and “confirmation stage” positive result) were calculated. Additionally, PODs were calculated for the reference method’s “confirmed” results (POD R ) at each level of inoculation and were compared to the PODs that were calculated for each level of inoculation for the candidate method where the “screening stage” and “confirmation stage” results were both positive for a particular sample (POD C ). The difference in POD for the two values at each level of inoculation were calculated (dPOD C ) along with its corresponding 95% confidence interval. As noted above, if the 95% confidence interval of a dPOD C value does not contain zero, then the difference between the POD C of the candidate method and the POD R of the reference method at that level of inoculation is statistically significant at the 5% level. The objective of this study was to validate the 3M TM MDA for the detection of E. coli O157:H7 in frozen blueberries. The inoculum concentration of E. coli O157:H7 was determined from Most Probable Number analysis, along with the 95% confidence intervals, as shown in Table 1. These inoculation levels targeted were chosen in order to meet the targeted POD values for the different inoculation levels. The concentrations achieved through inoculation were found to be 1.700 x 10 -2 MPN/g for the high inoculation level and 1.305 x 10 -2 MPN/g for the low inoculation level, according to the MPN analysis (Table 1). All data obtained for the candidate method testing of frozen blueberries, ‘screening stage’ and ‘confirmation stage’ (25 g frozen blueberry analyzed by 3M TM MDA) is provided in Table 2. All data obtained for the reference method testing of frozen blueberries (25 g frozen blueberry analyzed by the FDA BAM Ch. 4A) is provided in Table 3. The number of true positives (samples with a 3.0 RESULTS

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