342 / 596
4
Receipt Confirmation form provided and fax or email it back to the study director.The shipment
1
and hold timesof the inoculated test material had been verified as a quality control measure prior
2
to study initiation.
3
4
Test Portion Analysis
5
6
Collaborators were instructed to follow the appropriate preparation and analysis as outlined in
7
the study protocol for each matrix for both the 3M MDA 2 -
Listeria
method and reference
8
method. For both matrices, each collaborator received 72 test portions (12 high, 12 low and 12
9
un-inoculated controls for each method to be performed). For the analysis of the deli turkey test
10
portions by the 3M MDA 2 -
Listeria
method, a 125 g portion was enriched with 975 mL of
11
Demi-Fraser (DF) broth, homogenized for 2 minutes and incubated for 24-28 hours at 37 ±1
o
C.
12
For the raw chicken breast fillettest portions analyzed by the 3M MDA 2 -
Listeria
method, a 25
13
g portion was enriched with 475 mL of DF, homogenized for 2 minutes and incubated for 28-32
14
hours at 37 ±1
o
C.
15
Following enrichment, samples were assayed by the 3M MDA 2 -
Listeria
method and,
16
regardless of presumptive result, confirmed following the USDA/FSIS MLG 8.09 reference
17
method. Both matrices evaluated by the 3M MDA 2 -
Listeria
method were compared to
18
samples analyzed using the USDA/FSIS MLG 8.09 reference method in an unpaired study
19
design. All positive test portions were biochemically confirmed by the API
Listeria
biochemical
20
test or by the VITEK 2 GPbiochemical identification test, AOAC Official Method 2012.02 [8].
21
22
Statistical Analysis
23
24
Each collaborating laboratory recorded results for the reference method and the 3M MDA 2 -
25
Listeria
method on the data sheets provided. The data sheets were submitted to the study director
26
at the end of each week of testing for statistical analysis. Data for each matrix was analyzed
27
using the probability of detection (POD)statistical model [9]
.
.
POD statistical analysis was
28
conducted using AOAC Binary Data Interlaboratory Study Workbook, Version 2.3 [10].
The
29
probability of detection (POD) was calculated as the number of positive outcomes divided by the
30
total number of trials. The POD was calculated for the candidate presumptive results, POD
CP,
the
31
candidate confirmatory results (
excluding those with presumptive negative resultsincluding false
32
negative results
), POD
CC
, the difference in the candidate presumptive and confirmatory results,
33
dLPOD
CP,
presumptive candidate results that confirmed positive (
(including those with
34
presumptive negative results)excluding false negative results)
, POD
C,
the reference method,
35
POD
R
, and the difference in the confirmed candidate and reference methods, dLPOD
C
. A
36
dLPOD
C
confidence interval not containing the point zero would indicate a statistically
37
significant difference between the 3M MDA 2 -
Listeria
and the reference methods at the 5 %
38
probability level. In addition to POD, the repeatability standard deviation (s
r
), the among
39
laboratory repeatability standard deviation (s
L
), the reproducibility standard deviation (s
R
)and the
40
P
T
value were calculated. The s
r
provides the
variance variability
of data within one laboratory,
41
the s
L
provides the difference in standard deviation between laboratories and the s
R
provides the
42
variance variability
in data between different laboratories. The P
T
value provides information on
43
the homogeneity test of laboratory PODs
[10]
.
44
45
46
47
48
49