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1-5% (v:v in water) household bleach solution for 1 hour and away from the assay
1
preparation area.
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NOTICE:
To minimize the risk of false positives due to cross-contamination, never open reagent tubes
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containing amplified DNA. This includes Reagent Control, Reagent and Matrix Control tubes. Always
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dispose of sealed reagent tubes by soaking in a 1-5% (v:v in water) household bleach solution for 1 hour
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and away from the assay preparation area.
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H.
RESULTS AND
INTERPRETATION
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An algorithm interprets the light output curve resulting from the detection of the nucleic acid
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amplification. Results are analyzed automatically by the software and are color-coded based
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on the result. A Positive or Negative result is determined by analysis of a number of unique
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curve parameters. Presumptive positive results are reported in real-time while Negative and
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Inspect results will be displayed after the run is completed. Presumptive positive results
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should be confirmed using your preferred method or as specified by local regulations
.
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NOTE:
Even a negative sample will not give a zero reading as the system and 3M Molecular Assay
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Salmonella
amplification reagents have a “background” relative light unit (RLU).
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In the rare event of any unusual light output, the algorithm labels this as “Inspect.” 3M
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recommends the user to repeat the assay for any Inspect samples. If the result continues to
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be Inspect, proceed to confirmation test using your preferred method or as specified by local
23
regulations
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Results of Collaborative Study
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In this collaborative study, the 3M Molecular Detection Assay (MDA)
Salmonella
method was
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compared to the to the USDA/FSIS-MLG 4.05 reference method for raw ground beef and to the
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FDA/BAM Ch. 5 reference method for wet dog food. A total of 20 laboratories throughout the
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United States participated in this study, with 14 laboratories submitting data for the raw ground
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beef and 16 laboratories submitting data for the wet dog food as presented in Table 1. Each
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laboratory analyzed 36 test portions for each method: 12 inoculated with a high level of
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Salmonella
, 12 inoculated with a low level of
Salmonella
, and 12 un-inoculated controls. For
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each matrix, the actual level of
Salmonella
was determined by MPN determination on the day of
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initiation of analysis by the coordinating laboratory. The individual laboratory and sample
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results are presented in Tables 2-3. Table 2013.1A-B summarizes the inter-laboratory results for
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all foods tested, including POD statistical analysis [10]. The results of the collaborating
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laboratories aerobic plate count analysis for each matrix is presented in Table 2013.2C of the
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Appendix.
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Raw Ground Beef (25 g Test Portions)
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Raw ground beef test portions were inoculated at a low and high level and were analyzed
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(Table 2) for the detection of
Salmonella
spp. Un-inoculated controls were included in each
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analysis. The results presented for the raw ground beef were from a second shipment of test
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portions to the collaborating laboratories. The initial shipment of raw ground beef test portions
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