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Shelf Life and Lot-to-Lot Consistency Results
2
Results for the 3M Molecular Detection Assay
Salmonella
lot to lot/consistency study are summarized
3
in Table 5 in the appendix. Both
Salmonella
strains were positive for all replicates tested showing no
4
differences between lots or kit age. The
C. freundii
strain was negative for all replicates.
5
6
Method Comparison
7
The 3M
™
Molecular Detection Assay
Salmonella
method was compared to the FDA/BAM
8
Chapter 5
Salmonella
(2)
reference method
for raw shrimp, bagged spinach, and wet pet food, and to
9
the USDA/FSIS MLG 4.05
Isolation and Identification of Salmonella from Meat, Poultry, Pasteurized
10
Egg, and Catfish Products
(1) reference method for raw ground beef, cooked breaded chicken and
11
pasteurized liquid whole egg.
12
13
Each matrix was inoculated with a different strain of
Salmonella
serotypes as indicated in Table 6 of
14
the Appendix. A diluted 24 hour broth culture inoculum was added to a bulk sample of each lot of raw
15
ground beef, cooked breaded chicken, pasteurized liquid whole eggs, raw shrimp, bagged spinach, and
16
wet pet food and mixed thoroughly. The cooked breaded chicken, pasteurized liquid whole eggs and
17
raw shrimp were inoculated with an organism that had been heat stressed for 10 minutes at 50 ± 0.2
o
C
18
in a water bath. The degree of injury of the culture was estimated by plating an aliquot of diluted
19
culture onto Xylose Lysine Desoxycholate (XLD) and Tryptic Soy agar (TSA). The agars were incubated
20
at 37 ± 1°C for 24 ± 2 hours and the colonies were counted. The degree of injury was estimated
21
as
100 )
1(
x
n
n
nonselect
select
−
, where
n
select
= number of colonies on selective agar and
n
nonselect
= number of colonies
22
on nonselective agar. Results of the percent injury are presented in Table 6 of the Appendix. Following
23
inoculation, all test portions were mixed thoroughly, and were held at 2-5°C for 48-72 hours prior to
24
analysis to allow time for the organisms to equilibrate within the sample. Fractionally positive results,
25
those in which ether the reference or candidate method yields 5 to 15 positive results out of the 20
26
low level inoculum replicates, was required for each matrix.
27
28
The level of
Salmonella
was determined by Most Probable Number (MPN) on the day of analysis by
29
analyzing 3 x 100 g, 3 x 10 g, 3 x 1.0 g, and 3 x 0.1 g inoculated test samples. Each test portion was
30
enriched with the appropriate reference method enrichment broth at a 1:10 dilution and analyzed by
31
the reference method procedure. The number of positives from the 4 test levels was used to calculate
32
the MPN using Appendix 2: Most Probable Number of Serial Dilutions from the FDA/BAM
10
.
33
34
A background screen of each matrix was conducted prior to inoculation and no natural contamination
35
of the target organisms was detected in the test matrices.
36
37
3M
™
Molecular Detection Assay
Salmonella
Method Comparison
(See Figures 1 and 2 in Appendix)
38
39
USDA/FSIS-MLG 4.05 Isolation and Identification of Salmonella from Meat, Poultry, Pasteurized Egg
40
and Catfish.
41
For the USDA/FSIS method, all test portions for each food product, raw ground beef, cooked breaded
42
chicken, and pasteurized liquid whole eggs were prepared as described above. Following equilibration
43
of the microorganism in the matrix, 25 test portions consisting of 25 g for raw ground beef were added
44
to 225 mL of Buffered Peptone Water (BPW). For cooked breaded chicken, 25 test portions consisting
45
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