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For samples analyzed using the USDA/ FSIS-MLG 8.09 reference method, 125g test portions
1
were enriched with 1125 ± 25 mL of modified University of Vermont broth (UVM),
2
homogenized for 2 ± 0.5 minutes and incubated for 24 hours at 30 ± 2
o
C. After incubation,
3
samples were confirmed by streaking an aliquot of the primary enrichment onto MOX and
4
transferring an aliquot into FB. Presumptive positive samples were streaked for isolation
5
ontoHL and confirmed by evaluation of a hemolytic reaction and biochemically confirmed by
6
the VITEK 2 GP Biochemical Identification methodor API Listeria Identification System
7
biochemical test kits. Laboratories utilizing API Listeria kits were also required to conduct
8
catalase and oxidase tests.
9
10
11
12
Statistical Analysis
13
14
Each collaborating laboratory recorded results for the reference method and the 3M MDA
15
Listeriamonocytogenes
method on the data sheets provided. The data sheets were submitted to
16
the study director at the end of testing for analysis. The results of each test portion for each
17
sample were compiled by the study director and the 3M MDA
Listeria monocytogenes
results
18
were compared to the reference methods for statistical analysis. Data for each test portion size
19
was analyzed using the probability of detection (POD) [9]. The probability of detection (POD) is
20
the proportion of positive analytical outcomes for a qualitative method for a given matrix at a
21
given analyte level or concentration. POD is concentration dependent.
The POD was calculated
22
for the candidate presumptive results, POD
CP,
the candidate confirmatory results (including false
23
negative results), POD
CC
, the difference in the candidate presumptive and confirmatory results,
24
dPOD
CP,
presumptive candidate results that confirmed positive (excluding false negative results),
25
POD
C,
the reference method, POD
R
, and the difference in the confirmed candidate and reference
26
methods, dPOD
C
. A dLPOD confidence interval not containing the point zero would indicate a
27
statistically significant difference between the 3M MDA
Listeria monocytogenes
and the AOAC
28
OMA 993.12 reference methods at the 5 % probability level. In addition to POD, the
29
repeatability standard deviation (s
r
), the among laboratory repeatibilty standard deviation (s
L
),
30
the reproducibility standard deviation (s
R)
and the P
T
value were calculated. The s
r
provides
31
thevariance of data within one laboratory, the s
L
provides the difference in standard deviation
32
between laboratories and the s
R
provides the variance in data between different laboratories. The
33
P
T
value provides information on thehomogeneity test of laboraotory PODs[10].
34
35
36
37
38
39
40
41
42
43
44
45
46
AOAC Official Method 2014.xxx
47
Listeria monocytogenes
in Selected Foods and Environmental Surfaces
48
Candidates for 2016 Method of the Year
151