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Full fat cottage cheese test portions were inoculated at a low and high level and were
1
analyzed (Table 2) for the detection of
Listeriamonocytogenes
. Un-inoculated controls were
2
included in each analysis. Fifteen Laboratories participated in the evaluation of the full fat
3
cottage cheese. Laboratories 4 and 5 did not submit results to the coordinating laboratory.
4
Laboratories 6 and 13 reported deviations in the protocol (laboratory6 incorrectly incubated their
5
MDA test portions at 30
o
C instead for 48 hours instead of the required 37
o
C for 24 hours;
6
laboratory 13 confirmed all colony growthregardless of supplementary test results (Gram stain,
7
catalase reaction) indicating that the organism would not be classified as
Listeria
(Gram negative
8
or Gram positive with spores, catalase negative))and results from these laboratories were
9
excluded from the statistical analysis. The MPN levels obtained for this test portion, with 95%
10
confidence intervals, were 0.80 CFU/test portion (0.63, 1.00) for the low level and 4.83 CFU/test
11
portion (3.30, 7.70) for the high level.
12
For the high level, 129 out of 132 test portions (POD
CP
of 0.98) were reported as presumptive
13
positive by the 3M MDA
Listeriamonocytogenes
method with all 132 test portions (POD
CC
of
14
1.00) confirming positive. Based on the valid data submitted from each of the collaborating
15
laboratories, 3 false negative results were obtained resulting in 129 confirmed positives (POD
C
16
of 0.98). [Using the POD statistical analysis, only presumptive positive samples that confirmed
17
positive are used to calculate POD
C
.] For the low level, 66 out of 132 test portions (POD
CP
of
18
0.50) were reported as presumptive positive by the 3M MDA
Listeria monocytogenes
method
19
with 64 test portions (POD
CC
of0.48) confirming positive. Based on the valid data submitted
20
from each of the collaborating laboratories, 3 false positive results and 1 false negative result
21
were obtained resulting in 63 confirmed positives (POD
C
of 0.47).For the un-inoculated controls,
22
0 out of 132 samples produced a presumptive positive result by the 3M MDA
Listeria
23
monocytogenes
method with all test portions confirming negative. For test portions analyzed by
24
the AOAC 993.12 Method, 132 out of 132 high leveltest portions (POD
R
of 1.00) and 73 out of
25
132 low leveltest portions (POD
R
of 0.55) confirmed positive. For the un-inoculated controls, 0
26
out of 132 test portions (POD
R
of 0.00) confirmed positive.
27
For the low level, a dLPOD
C
value of -0.08 with 95% confidence intervals of
28
(-0.20, 0.05) were obtained between the 3M MDA
Listeriamonocytogenes
method and the AOAC
29
OMA 993.12 method. The confidence intervals obtained for dLPOD
C
indicated no significant
30
difference between the two methods. A dLPOD
CP
value of 0.02 with 95% confidence intervals
31
of (-0.11, 0.14) were obtained between presumptive and confirmed 3M MDA
32
Listeriamonocytogenes
results. The confidence intervals obtained for dLPOD
CP
indicated no
33
significant difference between the presumptive and confirmed results using either confirmation
34
process.
35
For the high level, a dLPOD
C
value of -0.02 with 95% confidence intervals of
36
(-0.06, 0.01) were obtained between the 3M MDA
Listeria monocytogenes
method and the
37
AOAC OMA 993.12 method. The confidence intervals obtained for dLPOD
C
indicated no
38
significant difference between the two methods. A dLPOD
CP
value of -0.02 with 95%
39
confidence intervals of (-0.06, 0.01) were obtained between presumptive and confirmed 3M
40
MDA
Listeriamonocytogenes
results. The confidence intervals obtained for dLPOD
CP
indicated
41
no significant difference between the presumptive and confirmed results. Detailed results of the
42
POD statistical analysis are presented in Table 2014.2A and Figures 1A-1B of the
43
Supplemenatary materials.
44
45
46
Deli Turkey Results (125 g Test Portions)
47
48
Candidates for 2016 Method of the Year
159