353 / 596
15
analysis. Laboratory 11 did not participate in the evaluation of this matrix. Laboratory 10
1
submitted data that indicated cross contamination of the inoculating organism in the un-
2
inoculated control samples. Further analysis at the coordinating laboratory confirmed the cross
3
contamination of the un-inoculated controls. Due to this issue, the data submitted from
4
Laboratory 10 was not used in the statistical analysis. All other laboratories submitted data for
5
both methods evaluated.The MPN levels obtained for this matrix, with 95% confidence intervals,
6
were 0.66 CFU/test portion (0.51, 0.83) for the low level and 6.24 CFU/test portion (3.58, 10.88)
7
for the high level.
8
For the low inoculum level, 88 out of 132 test portions (POD
CP
of 0.67) were reported as
9
presumptive positive by the 3M MDA 2 –
Listeria
method with 86out of 132 test portions
10
(POD
CC
of 0.65) confirming positive. For samples that produced presumptive positive results on
11
the 3M MDA 2 –
Listeria
method, 85out of 132 test portions confirmed positive (POD
C
of 0.64).
12
For test portions evaluated by the USDA/FSIS MLGreference method, 64 out of 132 test
13
portions produced positive results. A dLPOD
C
value of 0.16 with 95% confidence intervals of
14
(0.04, 0.28) was obtained between the candidate and reference method, indicating a statistically
15
significant difference between the two methods, with a
nobserved higher proportion of positive
16
results by the candidate method than the reference method.positive with a positive correlation in
17
data indicating more recovery of the target analyte by the candidate method.
A dLPOD
CP
value of
18
0.02 with 95% confidence intervals of (-0.10, 0.13) was obtained between presumptive and
19
confirmed results indicating
the difference between presumptive and confirmed results was not
20
statistically significant at the 0.05 probability
level.nostatistically significant difference between
21
the presumptive and confirmed results.
22
For the high inoculum level, 131 out of 132 test portions (POD
CP
of 0.99) were reported as
23
presumptive positive by the 3M MDA 2 –
Listeria
method with 132out of 132 test portions
24
(POD
CC
of 1.00) confirming positive. For samples that produced presumptive positive results on
25
the 3M MDA 2 –
Listeria
method, 131out of 132 samples confirmed positive (POD
C
of 0.99).
26
For test portions evaluated by the USDA/FSIS-MLG reference method, 132 out of 132 test
27
portions produced positive results. A dLPOD
C
value of -0.01 with 95% confidence intervals of
28
(-0.04, 0.02) was obtained between the candidate and reference method, indicating
the difference
29
between methods was not statistically significant at the 0.05 probability level. no statistically
30
significant difference between the two methods.
A dLPOD
CP
value of -0.01 with 95%
31
confidence intervals of (-0.04, 0.02) was obtained between presumptive and confirmed results
32
indicating
the difference between presumptive and confirmed results was not statistically
33
significant at the 0.05 probability
level.nostatistically significant difference between the
34
presumptive and confirmed results.
35
For the un-inoculated controls, 2 out of 132 samples (POD
CP
of 0.02) produced a presumptive
36
positive result by the 3M MDA 2 -
Listeria
method with 1 out of a 132 test portions (POD
CC
of
37
0.01) confirming positive. For samples that produced presumptive positive results on the 3M
38
MDA 2 –
Listeria
method, 1 out of 132 samples confirmed positive (POD
C
of 0.01). For test
39
portions evaluated by the USDA/FSIS-MLG reference method, 0 out of 132 test portions
40
produced positive results. A dLPOD
C
value of 0.01 with 95% confidence intervals of (-0.02,
41
0.04) was obtained between the candidate and reference method, indicating
the difference
42
between methods was not statistically significant at the 0.05 probability
level.nostatistical
43