AOAC-RI ERP Book Micro Jan 19 2017

reference method at that level of inoculation is statistically significant at the 5% level.

3.0 RESULTS The objective of this study was to validate the 3M™ Molecular Detection Assay (MDA) for the detection of E. coli O157:H7 in ground beef. 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. All data obtained for the candidate method testing of ground beef enriched for 18 hr, ‘screening stage’ and ‘confirmation stage’ (325 g ground beef analyzed by the 3M TM MDA) is provided in Table 2. All data obtained for the reference method testing of ground beef (325 g ground beef analyzed by the USDA FSIS MLG Method 5.09) is provided in Table 3. The number of true positives (samples with a positive ‘screening stage’ and a positive ‘confirmation stage’), true negatives (samples with a negative ‘screening stage’ and a negative ‘confirmation stage’), false positive (samples with a positive ‘screening stage’ but a negative ‘confirmation stage’) and false negatives (samples with a negative ‘screening stage’ but a positive ‘confirmation stage’ ) for the candidate method testing of ground beef enriched for 18 hr is provided in Table 4. As described in Section 2.7, the results presented here were statistically analyzed according to the POD methods of the 2012 version of the AOAC International Methods Committee Guidelines for Validation of Microbiological Methods for Food and Environmental Surfaces document (1). The POD CP , POD CC , dPOD CP , POD C , POD R , and dPOD C values calculated at each level of inoculation for the candidate method and the reference method testing of ground beef, and their corresponding 95% confidence intervals, are provided below in Table 5 for the ground beef samples enriched for 18 hr.

Table 1. Concentration of E. coli O157:H7 Inoculum Level per Gram of Matrix, Determined through Most Probable Number Analysis

Sample Size Sample NumberNumber of Positives MPN/g 1

95% CI 1

Food Matrix/Inoculation Level

650 325 162 650 325 162

5

1

1.739 X 10 -3

9.882 X 10 -4 , 2.808 X 10 -3

Ground Beef/Low

20

11

5 5 5 5

2 5 5 5

1.538 X 10 9

6.318 X 10 -3 , 1.5380 9

Ground Beef/High

1. MPN/g and 95% Confidence Interval Values were generated from the LCF MPN Calculator Version 1.6

CONFIDENTIAL INFORMATION Page 6 of 13