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stomacher for 2 minutes. For the analysis of cooked breaded chicken, 325 g test portions were
1
enriched with 2925 mL of 3M BPW ISO. For the analysis of pasteurized liquid whole eggs, 100 g test
2
portions were enriched with 900 mL of 3M BPW ISO. For the analysis of wet pet food, 375 g samples
3
were enriched with 3375 mL of 3M BPW ISO. Cooked breaded chicken, pasteurized liquid whole eggs
4
and wet pet food samples were massaged by hand for 2 minutes. All samples were incubated at 37 ±
5
1
o
C for 18-24 hours.
6
7
Prior to analysis, lysis tubes were brought to room temperature (25 ± 2
o
C) by placing the tubes on a
8
sanitized bench top for 18 ± 2 hours. After incubation, test samples were mixed by shaking. Using the
9
3M
™
Molecular Detection System software, prompts were followed to identify samples and controls.
10
11
A 20 µL aliquot of each sample and 20 µL of NC were transferred to separate lysis tubes and tubes
12
were mixed by inverting 3 times, ensuring that the resin in the bottom of the lysis tubes was dispersed
13
throughout the sample. After mixing, samples were placed on a dry bath incubator for 15 minutes at
14
100 ± 1
o
C. Following the heat lysis, samples were transferred to a cooling block and were allowed to
15
cool for 10 minutes. After cooling, samples were mixed by inverting 3 times and the lysis rack was
16
firmly tapped onto a sanitized bench top 3 times to settle the resin. Samples were allowed to sit
17
undisturbed on the bench top for 5 minutes.
18
19
A 20 µL aliquot of each lysed sample and control was added to separate reagent tubes and samples
20
were mixed by pipetting up and down 5 times, while care was taken to avoid creating bubbles. A 20 µL
21
aliquot of NC lysate was added to a RC tube. One 3MMolecular Detection Matrix Control tube was
22
analyzed along with the samples for each of the six matrices to verify that there was no interference
23
with the assay caused by the matrix. A 20 µL aliquot of a randomly picked lysed sample was added to
24
the matrix control tube, mixed, and recapped. All samples were loaded into the Speed Loader Tray
25
(SLT), placed into the 3M Molecular Detection System, and the 3M Molecular Detection Assay
26
Salmonella
was
initiated and results obtained within 75 minutes.
27
28
All primary enrichments, regardless of presumptive results, were transferred to the secondary
29
enrichment specified by each reference method. Samples were confirmed following procedures
30
outlined in the reference method and by the traditional biochemical tests for
Salmonella
specified by
31
each reference method including somatic O and flagellar H tests. Final confirmation was achieved by
32
VITEK 2 GN conducted per AOAC Official Method 2011.17.
33
34
RESULTS AND DISCUSSION
35
For the method comparison, results obtained from samples analyzed by the 3M Molecular Detection
36
Assay
Salmonella
method were comparable to those analyzed by the FDA/BAM Chapter 5 and
37
USDA/FSIS-MLG 4.05 reference methods (Table 6 in Appendix). A Mantel-Haenszel Chi-square analysis
38
(for unmatched test portions) between the 3M Molecular Detection Assay
Salmonella
samples and the
39
reference method samples indicated that there was no statistically significant difference between the
40
two methods.
41
42
It was determined that there was no matrix interference based on the results of the 3M™ Molecular
43
Detection Matrix Control test for any of the 6 matrices evaluated.
44
45
Raw Ground Beef
46
14