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February 20, 2013

15

Ruggedness Testing Results

1

Results for the 3M Petrifilm SALX System ruggedness study are summarized in Tables 4-7 in the Appendix.

2

Both

Salmonella

strains were positive for all replicates and method variations. The

Citrobacter braakii

3

strain was negative for all replicates and method variations.

4

5

Shelf Life and Lot-to-Lot Consistency Methodology

6

For the shelf life study, one lot of plates and disks was evaluated. Two more lots are being produced.

7

Results from the two new lots will be submitted with the yearly PTM renewal. The target shelf-life for the

8

3M Petrifilm SALX Plates and 3M Petrifilm SALX Confirmation Disks is 18 months.

9

10

Two serovars of

Salmonella

(

Salmonella

Typhimurium ATCC 14028 and

Salmonella

Poona NCTC 4840) and

11

one non-

Salmonella

strain (

Citrobacter braakii

ATCC 13048) were analyzed. Each organism was cultured in

12

3M Salmonella Enrichment with 3M Salmonella Enrichment Supplement and then diluted in the same broth

13

to within one log limit of detection of the method.

For each organism, five replicates of were tested (10

14

positive and 5 negative) using the 3M Petrifilm Salmonella Express System Method.

15

16

Shelf Life and Lot-to-Lot Consistency Results

17

Results presented are for shelf life of the one lot of 3M Petrifilm SALX plates and disks. Results are

18

summarized in Table 8 in the Appendix. Both

Salmonella

serovars were positive for all replicates

19

tested. The

Citrobacter braakii

strain was negative for all replicates.

20

21

3M Petrifilm Salmonella Express System Method-Reference Method Comparison

The 3M Petrifilm

22

Salmonella Express System was compared to the FDA/BAM Chapter 5

Salmonella

reference method (3)

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for shrimp, spinach, dry dog food, and stainless steel and to the USDA/FSIS MLG 4.0

5 Isolation and

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Identification of Salmonella from Meat, Poultry, Pasteurized Egg and Catfish Products

reference

25

method (4) for raw ground chicken, raw ground beef, raw ground pork, pasteurized liquid whole eggs,

26

and cooked chicken nuggets.

27

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Sample Preparation

29

The

Salmonella

cultures were prepared to deliver a target level of 0.2 - 2 CFU / test portion.

Each

30

matrix was inoculated with a different strain of

Salmonella

species. A diluted 24 hour broth culture

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inoculum was added to a bulk sample of each food matrix and mixed thoroughly. The cooked chicken

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nuggets and pasteurized liquid whole eggs were inoculated with an organism that had been heat

33

stressed for 10 minutes at 50

o

C in a water bath. The degree of injury of the culture was estimated by

34

plating an aliquot of diluted culture onto Xylose Lysine Desoxycholate (XLD) and Tryptic Soy agar (TSA).

35

The agars were incubated at 37° ± 1°C for 24 ± 2 hours and the colonies were counted. The degree of

36

injury was estimated as

100 )

1(

x

n

n

nonselect

select

, where

n

select

= number of colonies on selective agar and

37

n

nonselect

= number of colonies on nonselective agar. The matrix was well mixed and stored at 4°C for

38

48-72 hr to allow the inoculum to equilibrate with the food environment and to cold stress the cells.

39

The inoculated bulk samples were then used to generate all inoculated test portions. Ground beef test

40

samples of 325g and 375g were made with 25g of inoculated bulk and 300 grams or 350 grams,

41

respectively, of uninoculated bulk (3M and MLG samples). Inoculated and uninoculated portions were

42

well mixed to ensure homogeneity. At the time of enrichment, the inoculated products were randomly

43

split into test groups.

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