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B
ird
et al
.:
J
ournal of
AOAC I
nternational
V
ol
.
100, N
o
.
2, 2017
submitted no data. All other laboratories submitted data for
both methods evaluated. The MPN levels (with 95% confidence
intervals) obtained for this matrix 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, 69 of 132 test portions (POD
CP
of 0.52) were reported as presumptive positive by the 3M
MDA 2 –
Listeria monocytogenes
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 monocytogenes
method, 66 of 132 samples
confirmed positive (POD
C
of 0.50). For test portions
evaluated by the USDA/FSIS MLG reference method, 60 of
132 test portions produced positive results. A dLPOD
C
value
of 0.04 with a 95% confidence interval of (−0.08, 0.17) was
obtained between the candidate and reference methods,
indicating that the difference between methods was not
statistically significant at the 0.05 probability level. A dLPOD
CP
value of 0.02 with 95% confidence interval of (−0.10, 0.15) was
obtained between presumptive and confirmed results, indicating
that the difference between presumptive and confirmed methods
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 monocytogenes
method, with 132
of 132 test portions (POD
CC
of 1.00) confirming positive. For
samples that produced presumptive positive results on the 3M
MDA 2 –
Listeria monocytogenes
method, 132 of 132 samples
confirmed positive (POD
C
of 1.00). For test portions evaluated
by the USDA/FSIS MLG reference method, 132 of 132 test
portions produced positive results. A dLPOD
C
value of 0.00
with a 95% confidence interval of (−0.03, 0.03) was obtained
between the candidate and reference methods, indicating that
the difference between methods was not statistically significant
at the 0.05 probability level. A dLPOD
CP
value of 0.00 with a
95% confidence interval of (−0.03, 0.03) was obtained between
presumptive and confirmed results, indicating that 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 monocytogenes
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 monocytogenes
method, 0 of 132 samples
confirmed positive (POD
C
of 0.00). For test portions evaluated
by the USDA/FSIS MLG reference method, 0 of 132 test
portions produced positive results. A dLPOD
C
value of 0.00
with a 95% confidence interval of (−0.03, 0.03) was obtained
between the candidate and reference methods, indicating that
the difference between methods was not statistically significant
at the 0.05 probability level. A dLPOD
CP
value of 0.00 with
a 95% confidence interval of (−0.03, 0.00) was obtained
between presumptive and confirmed results, indicating that the
difference between presumptive and confirmed methods was
not statistically significant at the 0.05 probability level.
Detailed results of the LPOD statistical analysis are presented
in Table
2016.08C
and Figure 1.
Raw chicken breast fillet (25 g test portions)
.
—
Raw
chicken breast fillet test portions were inoculated at a low
and a high inoculum level and analyzed for the detection of
L. monocytogenes
. 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 of the inoculating organism in the uninoculated
control samples. Further analysis at the coordinating laboratory
confirmed the cross-contamination of the uninoculated controls.
Due to this issue, the data submitted from Laboratory 10 was not
used in the statistical analysis. All other laboratories submitted
data for both methods evaluated. The MPN levels obtained for
this matrix (with 95% confidence intervals) were 0.66 CFU/test
portion (0.51, 0.83) for the low inoculum level and 6.24 CFU/
test portion (3.58, 10.88) for the high inoculum level.
For the low inoculum level, 86 of 132 test portions (POD
CP
of 0.65) were reported as presumptive positive by the 3M MDA
2 –
Listeria monocytogenes
method, with 86 of 132 test portions
(POD
CC
of 0.65) confirming positive. For samples that produced
presumptive positive results on the 3M MDA 2 –
Listeria
monocytogenes
method, 85 of 132 test portions confirmed
positive (POD
C
of 0.64). For test portions evaluated by the
USDA/FSIS MLG reference method, 64 of 132 test portions
produced positive results. A dLPOD
C
value of 0.16 with a
95% confidence interval of (0.04, 0.28) was obtained between
the candidate and reference methods, indicating a statistically
significant difference between the two methods, with a higher
proportion of positive results observed with the candidate
method compared to the reference method. A dLPOD
CP
value
of 0.00 with a 95% confidence intervals of (−0.12, 0.12) was
obtained between presumptive and confirmed results, indicating
that the difference between presumptive and confirmed methods
was not statistically significant at the 0.05 probability level.
For the high inoculum level, 129 of 132 test portions
(POD
CP
of 0.98) were reported as presumptive positive by
the 3M MDA 2 –
Listeria monocytogenes
method, with 132
of 132 test portions (POD
CC
of 1.00) confirming positive. For
samples that produced presumptive positive results on the 3M
MDA 2 –
Listeria monocytogenes
method, 129 of 132 samples
confirmed positive (POD
C
of 0.98). For test portions evaluated
by the USDA/FSIS MLG reference method, 132 of 132 test
portions produced positive results. A dLPOD
C
value of −0.02
with a 95% confidence interval of (−0.06, 0.01) was obtained
between the candidate and reference methods, indicating that
the difference between methods was not statistically significant
at the 0.05 probability level. A dLPOD
CP
value of −0.02 with
a 95% confidence interval of (−0.06, 0.01) was obtained
between presumptive and confirmed results, indicating that the
difference between presumptive and confirmed methods 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 monocytogenes
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 monocytogenes
method, 0 of 132 samples confirmed
positive (POD
C
of 0.00). For test portions evaluated by the
USDA/FSIS MLG reference method, 0 of 132 test portions
produced positive results. A dLPOD
C
value of 0.00 with a 95%
confidence interval of (−0.03, 0.03) was obtained between
the candidate and reference methods, indicating that the
difference between methods was not statistically significant
at the 0.05 probability level. A dLPOD
CP
value of 0.00 with
a 95% confidence interval of (−0.03, 0.00) was obtained