150 / 350
February 20, 2013
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For the analysis of the dry dog food test portions, a bulk lot of test product was inoculated with a
1
lyophilized culture and held at 25° ± 2
o
C for two weeks to allow time for the organism to equilibrate.
2
Test portions analyzed by the 3M Petrifilm SALX System were prepared by mixing 25 g of inoculated
3
test product with 350g of un-inoculated test product. Twenty-five grams of inoculated test product
4
were analyzed by the FDA/BAM method. For the analysis of the cooked chicken nuggets, 25 g of
5
inoculated test product was mixed with 300 g of un-inoculated test product and analyzed by both the
6
3M Petrifilm SALX System and USDA reference method.
7
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Environmental surfaces were inoculated at a level expected to yield fractional recovery. Replicate 4"x 4"
9
stainless steel surfaces areas were inoculated with 0.10 mL of diluted culture and dried for 16-24 hours at
10
room temperature (24° ± 2
o
C). The inoculation level for the stainless steel test portions was determined by
11
plating the inoculum onto Tryptic Soy agar (TSA) in triplicate. Sampling sponges, pre-moistened with Dey-
12
Engley neutralizing broth, were used to sample each test area using horizontal and vertical motions. The
13
sponges were held at room temperature for at least 2 hours prior to analysis.
14
15
A background screen of each food matrix was conducted prior to inoculation and no natural contamination
16
of the target organisms was detected in the test matrices.
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Most Probable Number (MPN) Determination
- The level of
Salmonella
was determined by Most Probable
19
Number (MPN) on the day of analysis by analyzing 3 x 100 g, 20 x 25 g (reference method test portions) and
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3 x 5.0 g inoculated test samples for the raw ground chicken, raw ground beef, raw ground pork, frozen
21
uncooked shrimp and fresh spinach. For the cooked chicken nuggets and dry dog food, 5 x 75 g, 5 x 25 g
22
(from the bulk lot of inoculated test product) and 5 x 10.0 g test portions were analyzed. For the
23
pasteurized liquid whole eggs, 5 x 200 g, the 20 reference method test portions and 5 x 25 g test portions
24
were analyzed. Each test portion was enriched with the appropriate reference method enrichment broth
25
at a 1:10 dilution and analyzed by the reference method procedure. The number of positives from the 3
26
test levels was used to calculate the MPN using the AOAC MPN calculator.
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(http://www.lcfltd.com/customer/LCFMPNCalculator.exe)28
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Anaytical Protocols
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USDA/FSIS-MLG 4.05 Isolation and Identification of Salmonella from Meat, Poultry, Pasteurized Egg and
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Catfish.
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For the USDA/FSIS method, all test portions for each food product, raw ground chicken, pasteurized liquid
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whole eggs, raw ground beef, raw ground pork and cooked chicken nuggets were prepared as outlined in
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the study protocol. Following equilibration of the microorganism in the matrix, 25 test portions consisting
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of 25 g for raw ground chicken, raw ground beef and raw ground pork were enriched with 225 mL of
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Buffered Peptone Water (BPW) and homogenized for 2 minutes. For cooked chicken nuggets, 25 test
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portions consisting of 325 g were enriched with 1500 mL of BPW and homogenized for
44
2 minutes. After mixing, an additional 1425 mL of BPW was added to the sample. For pasteurized liquid
45
whole eggs, 25 test portions of 100 g were enriched with 900 mL of BPW and homogenized for
46
2 minutes. All test portions were incubated at 35° ± 2°C for 20-24 hours.
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