421 / 596
1
For the low invocation level, a POD value of 0.50 was obtained with a 95% confidence interval
2
of (0.24, 0.76). All 5 non-target test portions were negative with a POD value of 0.00 with a 95%
3
confidence interval of (0.00, 0.43).
4
5
Independent Laboratory Observations
6
7
The results of this study demonstrate the ability of the MDA 2 -
Listeria
to detect the presence of
8
Listeria
in various food matrixes and select environmental surfaces after 24-28 hours of a
9
primary enrichment. The MDA 2 -
Listeria
offers the benefits of extremely high sensitivity and
10
high specificity for the detection of
Listeria
while reducing the overall time to presumptive
11
results. The MDA 2 -
Listeria
also reduces the total analyst time required to obtain final results
12
by implementing a single heat lysis step and cool step, followed up by a single transfer to
13
molecular reaction tubes. The small footprint of the Molecular Detection System requires only
14
minimal lab and bench space, making it easy to move the instrument or pair up additional MDS
15
units to perform multiple MDA runs concurrently. The updated software is user friendly with
16
easy to interpret results. The ability to examine Relative Light Unit (RLU) curves makes trouble
17
shooting more streamlined if any problems occur while testing is being conducted.
18
19
Discussion
20
21
All matrixes evaluated in this validation study, including the raw chicken, resulted in no
22
statistical differences when compared to the reference methods. Three different brands of Demi
23
Fraser with FAC were used in this study, referred to as X, Y, and Z.
24
25
There were no differences between the 24 and 26 hour primary enrichment time points for the
26
environmental surfaces tested, therefore a 24 hour minimum enrichment time will be
27
recommended for these matrixes: stainless steel, sealed concrete and plastic.
28
29
The five false negative results with raw chicken (leg pieces) evaluated in the internal study
30
resulted in an investigation of protocol. It was determined that the contract laboratory
31
conducting the study used Demi Fraser with FAC brand X, which demonstrated low
32
productivity. Brand X had also been used to analyze the inclusive list, spinach, and cold smoked
33
salmon.
34
35
When the protocol for raw chicken was performed at the independent laboratory, using a
36
different brand Y, two lots of naturally contaminated raw chicken (leg pieces) analyzed showed
37
no statistical difference when compared to the reference method. Lot 1 of the naturally
38
contaminated raw chicken (leg pieces) had zero false negatives, while Lot 2 had two false
39
negatives.
40
41
To expand the robustness of the method to include multiple raw chicken matrixes, raw chicken
42
fillets were chosen and brand Z was used. The raw chicken (fillet) testing resulted in no
43
statistical difference when compared to the reference method, which highlighted the importance
44
of internally validating any method as a system within one’s own laboratory. This is why 3M
45
has always emphasized this advisory within our package inserts;
46