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ird
et al
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nternational
V
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1, 2017
assay for any Inspect samples. If the result continues to read
“Inspect,” proceed to the confirmation test using your preferred
method or as specified by local regulations.
Results of the Collaborative Study
For this collaborative study, the 3M MDA 2–
Listeria
method
was compared with the USDA/FSIS MLG 8.09 reference
method for deli turkey and raw chicken breast fillet. A total
of 13 laboratories throughout the United States and Canada
participated in this study, with 11 laboratories submitting data
for the deli turkey and 12 laboratories submitting data for the
raw chicken breast fillet.
See
Table 2 for a summary of laboratory
participation for each matrix. Each laboratory analyzed 36 test
portions for each method per matrix: 12 inoculated with a high
level of
Listeria
, 12 inoculated with a low level of
Listeria
, and
12 uninoculated controls.
A background screen of the matrix indicated an absence of
indigenous
Listeria
species in both matrixes. Ten replicate test
portions (randomly sampled from 50% of the total packages used
in the analysis) were screened for the presence of
Listeria
species.
All test portions produced negative results for the target analyte.
Results for the heat-stress analysis of the inoculum for the
deli turkey are presented in Table 1. The raw chicken breast
fillet was not heat-treated, therefore it was not necessary to
injure the cells. Tables
2016.07A
and
2016.07B
summarize
the interlaboratory results for all foods tested, including POD
statistical analysis. As per criteria outlined in Appendix J of the
AOAC validation guidelines (4), fractional positive results were
obtained. Detailed results for each laboratory are presented in
Tables
2016.07C
and
2016.07D
. For each matrix, the level
of
Listeria
was determined by MPN on the day of initiation
of analysis by the coordinating laboratory. MPN results are
presented in Tables
2016.07C
and
2016.07D
. The individual
laboratory and sample results are presented in Tables 1 and 2 in
Supplemental Information
.
(a)
Deli turkey (125g test portions)
.
—
Deli turkey test portions
were inoculated at a low and high level and were analyzed for the
detection of
Listeria
spp. Uninoculated controls were included
in each analysis. Laboratories 8 and 10 received test portions
but were unable to conduct the analysis, and, therefore, no data
submitted. All other collaborating laboratories submitted data
for both methods under evaluation. The MPN levels obtained for
this matrix with 95% confidence intervals were 0.63 CFU/test
portion (0.49, 0.80) for the low inoculum level and 4.52 CFU/test
portion (3.19, 6.42) for the high inoculum level.
For the low inoculum level, 68 of 132 test portions (POD
CP
of 0.52) were reported as presumptive positive by the 3M MDA
2–
Listeria
method, with 66 of 132 test portions (POD
CC
of 0.50)
confirming positive. For samples that produced presumptive
positive results on the 3M MDA 2–
Listeria
method, 66 of 132
samples confirmed positive (POD
C
of 0.50). For test portions
evaluated by the USDA/FSIS MLG 8.09 reference method,
60 of 132 test portions produced positive results. A dLPOD
C
value of 0.04 with 95% confidence intervals of (–0.08, 0.17)
was obtained between the candidate and reference methods,
indicating the difference between methods was not statistically
significant at the 0.05 probability level. A dLPOD
CP
value
of 0.02 with 95% confidence intervals of (–0.11, 0.14) was
obtained between presumptive and confirmed results, indicating
the difference between presumptive and confirmed results was
not statistically significant at the 0.05 probability level.
For the high inoculum level, 132 of 132 test portions (POD
CP
of 1.00) were reported as presumptive positive by the 3M
MDA 2–
Listeria
method, with 132 of 132 test portions (POD
CC
of 1.00) confirming positive. For samples that produced
presumptive positive results on the 3MMDA2–
Listeria
method,
132 of 132 samples confirmed positive (POD
C
of 1.00). For test
portions evaluated by the USDA/FSIS MLG 8.09 reference
method, 132 of 132 test portions produced positive results.
A dLPOD
C
value of 0.00 with 95% confidence intervals of
(–0.03, 0.03) was obtained between the candidate and reference
methods, indicating the difference between the methods was not
statistically significant at the 0.05 probability level. A dLPOD
CP
value of 0.00 with 95% confidence intervals of (–0.03, 0.03) was
obtained between presumptive and confirmed results, indicating
the difference between presumptive and confirmed results was
not statistically significant at the 0.05 probability level.
For the uninoculated controls, 0 of 132 samples (POD
CP
of
0.00) produced a presumptive positive result by the 3M MDA
2–
Listeria
method with 0 of 132 test portions (POD
CC
of 0.00)
confirming positive. For samples that produced presumptive
positive results on the 3M MDA 2–
Listeria
method, 0 of 132
samples confirmed positive (POD
C
of 0.00). For test portions
evaluated by the USDA/FSIS MLG 8.09 reference method,
0 of 132 test portions produced positive results. A dLPOD
C
value of 0.00 with 95% confidence intervals of (–0.03, 0.03)
was obtained between the candidate and reference methods,
indicating the difference between methods was not statistically
significant at the 0.05 probability level. A dLPOD
CP
value
of 0.00 with 95% confidence intervals of (–0.03, 0.00) was
obtained between presumptive and confirmed results, indicating
the difference between presumptive and confirmed results was
not statistically significant at the 0.05 probability level.
Detailed results of the POD statistical analysis are presented
in Table
2016.07C
and Figure 1A and B.
(b)
Raw chicken breast fillet (25 g test portions)
.
—
Raw
chicken breast fillet test portions were inoculated at a low and
high inoculum level and analyzed for the detection of
Listeria
spp. Uninoculated controls were included in each analysis.
Laboratory 11 did not participate in the evaluation of this matrix.
Laboratory 10 submitted data that indicated cross-contamination
Table 2. Participation of each collaborating laboratory
a,b
Lab
Deli turkey
Raw chicken breast fillet
1
Y
Y
2
Y
Y
3
Y
Y
4
Y
Y
5
Y
Y
6
Y
Y
7
Y
Y
8
N
Y
9
Y
Y
10
N
Y
11
Y
N
12
Y
Y
13
Y
Y
a
Y=The collaborator analyzed the food type.
b
N=The collaborator did not analyze the food type.