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DuPont™ BAX
®
System Real-Time PCR Assay for
Salmonella
: Collaborative Study
DuPont Nutrition & Health
Page 10
Red (+)
Positive for
Salmonella
Yellow (?) with red slash
Signal error
1
H.
Confirmation
2
Presumptive positive results are confirmed by culture and the biochemical and serological protocols
3
described in the appropriate reference method. For frankfurters, follow the USDA-FSIS Microbiology
4
Laboratory Guidebook (MLG) Chapter 4.05
(http://www.fsis.usda.gov/PDF/MLG_4_05.pdf). For orange
5
juice, follow the U.S. FDA Bacteriological Analytical Manual (FDA-BAM) Chapter 5
6
(http://www.fda.gov/Food/ScienceResearch/LaboratoryMethods/BacteriologicalAnalyticalManualBAM/7
ucm070149.htm).
8
Note: For the purposes of this study, all test method samples were confirmed with the appropriate confirmation method,
9
regardless of presumptive result.
10
Statistical Analysis
11
Data analysis was performed using each of the metrics below according to the format described in the
12
AOAC International Methods Committee Guidelines for Validation of Microbiological Methods for Food
13
and Environmental Surfaces and using the Least Cost Formulations, Ltd., AOAC Binary Data
14
Interlaboratory Study Workbook [6].
15
For the purposes of this evaluation, the probability of detection (POD) was defined as the number of
16
positive outcomes divided by the total number of trials. POD was estimated with a 95% confidence
17
interval for each of the following levels:
18
•
the candidate presumptive results (POD
CP
),
19
•
the candidate confirmatory results (POD
CC
),
20
•
the candidate method results based on the presumptive and confirmatory results (POD
C
)
21
•
the reference method results (POD
R
).
22
The candidate presumptive and confirmatory results were compared by determining the difference
23
between the POD values for each matrix and concentration (dLPOD
CP
= POD
CP
- POD
CC
). If the confidence
24
interval of a dLPOD does not contain zero, then the difference is statistically significant at the 5% level.
25
The candidate and reference method results were compared by determining the difference in POD
26
values between the candidate and reference methods for each matrix and concentration (dLPOD
C
=
27
POD
C
- POD
R
). If the confidence interval of a dLPOD does not contain zero, then the difference is
28
statistically significant at the 5% level.
29
Results and Discussion
30
The results for orange juice are summarized in Tables 1 – 3. At each inoculation level, the BAX® System
31
method and the reference method demonstrated no significant statistical difference as indicated by
32
FINAL (Version 4)