354 / 596
16
significant difference between the two methods.
A dLPOD
CP
value of 0.01 with 95% confidence
1
intervals of (-0.03, 0.05) was obtained between presumptive and confirmed results indicating
the
2
difference between presumptive and confirmed results was not statistically significant at the 0.05
3
probability
level.nostatistically significant difference between the presumptive and confirmed
4
results.
5
6
Detailed results of the POD statistical analysis are presented in Table 2016.2B and Figures 1C-
7
1D.
8
9
Discussion
10
11
No negative feedback was provided by the collaborating laboratories in regard to the
12
performance of the 3M MDA 2-
Listeria
method. During the evaluation of the raw chicken breast
13
fillet, Laboratory 2 isolated
Listeria innocua
from an un-inoculated control sample. Since the
14
organism recovered was different from the inoculating organism,
Listeria monocytogenes,
no
15
just cause for removal of the data was determined and the data was included in the manuscript.
16
For the raw chicken breast fillet, Laboratory 10 reported isolating
Listeria monocytogenes
from
17
two un-inoculated control samples. The isolates were sent for further identification and it was
18
determined that they were the same strain as the inoculating organism, indicating that cross
19
contamination of the sample occurred. Due to the fact that cross contamination occurred, just
20
cause removal of the data was established and the data generated by Laboratory 10 was therefore
21
not included in the statistical analysis.
22
Overall, the data generated during this evaluation demonstrates the reproducibility of this new
23
method. For the deli turkey analysis, the POD statistical analysis indicated
the difference
24
between the candidate method and reference method was not statistically significant at the 0.05
25
probability level. And that the difference between presumptive and confirmed candidate method
26
was not statistically significant at the 0.05 probability level.thatno statistically significant
27
difference between the candidate method and the reference method or between the presumptive
28
and confirmed results of the candidate method was obtained.
For raw chicken breast fillet, a
29
statistically significant difference was observed between the reference and the alternative
30
method.
The dLPOD being significantly greater than zero showed an observed higher proportion
31
of positive results by the candidate method than the reference method.The dLPOD data indicated
32
a positive correlation in data indicating more recovery of the target analyte by the candidate
33
method.
One possible contribution
for the higher observed proportion positive resultsto the
34
higher level of recovery
observed with the 3M MDA 2 –
Listeria
method was the use of Demi-
35
Fraser Broth for the candidate method. This enrichment media formulation is less selective than
36
the modified University of Vermont Medium used in the USDA reference method and may have
37
contributed to the higher level of recovery observed during the evaluation. A second possible
38
contribution
tfor the higher observed proportion positive resultso the higher level of recovery
39
was the length of the primary enrichment. Test portions evaluated by the 3M MDA 2 –
Listeria
40
method were incubated for a minimum of 28 hours in the primary enrichment, while the USDA
41
reference method had a maximum primary enrichment time of 26 hours. No statistically
42