AOAC-RI ERP Book MICRO Sept 2016.pdf

February 20, 2013

Statistical Analysis

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For the method comparison, results obtained from samples analyzed by the 3M Petrifilm SALX System were comparable to those analyzed by the FDA/BAM Chapter 5, USDA/FSIS-MLG 4.05 and ISO 6579 reference methods. A Mantel-Haenszel chi-square analysis (for unmatched test portions) was used to compare the 3MPetrifilm SALX System samples and the reference method samples. For the low inoculum level and the un-inoculated control level, the probability of detection (POD) was calculated as the number of positive outcomes divided by the total number of trials. The POD was difference in the candidate presumptive and confirmatory results, dPOD CP, POD R , and the difference in the confirmed candidate and reference methods, dPOD C were conducted for each time point and of the 3M Petrifilm SALX System and the reference methods. the reference method, . POD analyses Based on the results obtained from the MPN analyses, the target levels of 0.2-2 CFU/ test portion for the low inoculum level were achieved for each matrix tested. In addition, the requirement of obtaining fractionally positive results (5-15 positives out of 20 replicates) was achieved by either the candidate or reference methods or both for each of the matrices analyzed in this study. calculated for the candidate presumptive results, POD CP, the candidate confirmatory results, POD CC

, the

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RESULTS AND DISCUSSION

High Microbial Foods Raw Ground Chicken

For raw ground chicken test portions, there were 15 confirmed positives by the 3M Petrifilm SALX System at all four time points (18 hours and 24 hours of primary enrichment transferred into RV[R10] secondary enrichment and streaked at 8 and 24 hours) and 14 confirmed positives by the USDA/FSIS-MLG method. All un-inoculated control samples were negative by both methods. A χ 2 value of 0.12 was obtained between the reference methods and the candidate method when using the alternative confirmation indicating no significant difference between the candidate and reference method at all four time points. A χ 2 value of 0.0 was obtained between the reference method and the candidate method when using the traditional confirmation, indicating no significant difference between the candidate and reference method

at any of the time points.

For the low level inoculum, a dPOD C

value of 0.05 with 95% confidence intervals of (-0.22, 0.31) was

obtained between the USDA/FSIS-MLG reference method and the candidate method samples confirmed

using alternative confirmation at all four time points. A dPOD C

value of 0.00 with 95% confidence intervals

of (-0.26, 0.26) was obtained between the USDA/FSIS-MLG reference method and the candidate method samples confirmed using traditional confirmation at all four time points. The confidence intervals obtained

for the dPOD C

values indicated no significant difference between the two methods using either the

traditional or alternative confirmatory procedure. A dPOD CP

value of 0.00 with 95% confidence intervals of

(-0.26, 0.26) were obtained between presumptive and confirmed results using either the traditional or alternative confirmatory procedure at all four time points. The confidence intervals obtained for dPOD CP indicated no significant difference between the presumptive and confirmed results.

Frozen Uncooked Shrimp

For frozen uncooked shrimp test portions, there were 12 confirmed positives by the 3M Petrifilm SALX System at all four time points and 10 confirmed positives by the FDA/BAM method. All un-inoculated control samples were negative for both methods. A χ 2 value of 0.39 was obtained between the reference

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