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ird
et al
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J
ournal of
aoaC i
nternational
V
ol
.
99, n
o
.
4, 2016
991
(i)
After the assay is complete, remove the 3M Molecular
Detection speed loader tray from the 3M MDS instrument
and dispose of the tubes by soaking in a 1–5% (v/v in water)
household bleach solution for 1 h and away from the assay
preparation area.
Note:
To minimize the risk of false positives due to cross-
contamination, never open reagent tubes containing amplified
DNA. This includes RC, reagent, and matrix tubes. Always
dispose of sealed reagent tubes by soaking in a 1–5% (v/v in
water) household bleach solution for 1 h and away from the
assay preparation area.
J. Results and Interpretation
An algorithm interprets the light output curve resulting
from the detection of the nucleic acid amplification. Results
are analyzed automatically by the software and are color-
coded based on the result. A positive or negative result
is determined by analysis of a number of unique curve
parameters. Presumptive positive results are reported in real
time, whereas negative and “inspect” results will be displayed
after the run is completed. Presumptive positive results should
be confirmed using your preferred method or as specified by
the FDA BAM, USDA/FSIS MLG, or ISO 6579 reference
method, starting from the 3M primary enrichment, followed
by transfer to a secondary enrichment or direct plating onto
media through confirmation of isolates using appropriate
biochemical and serological methods.
Note:
Even a negative sample will not give a zero reading
because the system and 3M MDA 2 –
Salmonella
amplification
reagents have a “background” relative light unit reading.
In the rare event of any unusual light output, the algorithm
labels this as inspect. 3M recommends the user to repeat the
assay for any inspect samples. When the result continues to be
inspect, proceed to the confirmation test using your preferred
method or as specified by local regulations.
Results of Collaborative Study
For the collaborative study, the 3M MDA 2 –
Salmonella
method was compared to the USDA/FSIS MLG reference
method for raw ground beef and to the FDA BAM reference
method for creamy peanut butter. A total of 16 laboratories
throughout the United States participated in the study, with
13 laboratories submitting data for raw ground beef and
creamy peanut butter.
See
Table 1 for a summary of laboratory
participation for each matrix. Each laboratory analyzed 36
test portions for each method per matrix: 12 inoculated with
a high level of
Salmonella
, 12 inoculated with a low level of
Salmonella
, and 12 uninoculated controls.
A background screen of the matrix indicated an absence of
indigenous
Salmonella
spp. in both matrixes. Due to the amount
of raw ground beef needed for the evaluation (about1000 lb),
10 replicate 325 g test portions (prepared by compositing 65 g
from over 50% of the total packages used in the analysis)
were screened for
Salmonella
spp. All test portions produced
negative results for the target analyte. For creamy peanut butter,
10 replicate test portions (randomly sampled from 50% of
the total packages used in the analysis) were screened for the
presence of
Salmonella
spp. All test portions produced negative
results for the target analyte.
Results for the heat stress analysis of the inoculum for
the creamy peanut butter are presented in Table 2. The
individual laboratory and sample results are presented in
Tables 3 and 4. Tables
2016.01A
and
2016.01B
summarize
Figure 2016.01A.
Figure 2016.01B.
Table 1.
Participation of each collaborating laboratory
a
Laboratory
Raw ground beef
Creamy peanut butter
1
Y
Y
2
Y
Y
3
Y
Y
b
4
Y
Y
5
Y
c
Y
c
6
Y
Y
7
N
Y
b
8
Y
Y
9
Y
Y
10
N
Y
11
Y
Y
c
12
Y
Y
13
Y
Y
14
Y
Y
15
Y
Y
16
Y
N
a
Y = Collaborator analyzed the food type; N = collaborator did not
analyze food type.
b
Results were not used in statistical analysis due to laboratory error.
c
Results were not submitted to the coordinating laboratory.