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CONFIDENTIAL INFORMATION
Page 6 of 13
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
1. MPN/g and 95% Confidence Interval Values were generated from the LCF MPN Calculator Version 1.6
Food Matrix/Inoculation Level
Sample Size Sample NumberNumber of Positives MPN/g
1
95% CI
1
650
5
1
325
20
11
162
5
2
650
5
5
325
5
5
162
5
5
Ground Beef/Low
Ground Beef/High
1.739 X 10
-3
1.538 X 10
9
9.882 X 10
-4
, 2.808 X 10
-3
6.318 X 10
-3
, 1.5380
9