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3M Petrifilm SALX Collaborative Study
July 2013
OMA-2013-July-XXX
DRAFT DOCUMENT
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the correct contamination levels are achieved. Test portions (25g) will be pulled
1
from this bulk lot and randomly assigned to the reference method or the 3M
2
SALX method. An additional 350g uncontaminated dry dog food will be added
3
to the 25g test portion assigned to the 3M SALX method resulting in a 375g test
4
portion.
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4.3
Shipment of test portions.
Test portions will be packaged in leak-proof, insulated
7
containers and shipped (according to the Dangerous Goods Regulations IATA for
8
Infections Substances) by overnight carrier to arrive the day before initiation of analysis
.
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All refrigerated test portions will be packed with ice packs to maintain a temperature of
10
<7
°
C during transport. All dry test portions will be shipped at ambient temperature (22-
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25°C). A temperature control sample will be included with each shipment to verify
12
temperature of sample upon receipt. Upon arrival, the ground beef test portions will be
13
stored at 2-8
°
C until they are analyzed and the dry dog food test portions will be stored
14
at room temperature until they are analyzed.
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4.4
Microbiological analysis.
The test portion preparation is different for the 3M Petrifilm
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SALX and reference methods. Therefore, each collaborator will receive a separate test
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portion for each method. They will be instructed to test 25g ground beef using the 3M
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Petrifilm SALX method and another 25g ground beef using the MLG reference method.
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They will be instructed to test 375g dry dog food using the 3M Petrifilm SALX method
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and 25g dry dog food using the BAM reference method. All test portions assayed by the
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3M method will be confirmed following the reference method for confirmation of
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Salmonella
species as described in the Alternative Confirmation section. The Reference
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Method Confirmation procedures will be performed starting with the secondary
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enrichment steps. The recovered isolates will be identified by the API20E (Official
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Method 978.24) or the VITEK2 GN (Official Method 2011.17). The somatic (O) and
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flagellar (H) tests will also be performed.
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One additional control (negative) test portion will be provided to each collaborator for
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each matrix to determine the total plate count on the day of analysis.
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4.5
Most Probable Number (MPN) Analysis.
To determine the level of
Salmonella
spp
.
in
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the inoculated food test portions on the day of initiation of analysis, a 5-tube MPN
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determination is performed by the coordinating laboratory following the appropriate
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reference method. From each of the inoculated food batches, prepare 5 test portions of
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100 g, 5 test portions of 25 g and 5 test portions of 10 g. To each test portion, add BPW
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to make a 1:4 dilution. Follow the reference method through to confirmations. Use the
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number of positives from the high, medium and low levels to calculate the MPN for each
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inoculated level of each matrix. Access the MPN calculator
40
( http://www.lcfltd.com/customer/LCFMPNCalculator.exe )to determine the MPN values
41
and 95% confidence intervals. Data should be entered from high level to low. Report
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MPN as MPN/test portion.
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5.0
3M™ Petrifilm™ Salmonella Express (SALX) System Method
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5.1
Applicability
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OMAMAN-08/Collaborative Study Protocol
March 2014
Expert Review Panel Use Only
AOAC Research Institute
Expert Review Panel Use Only