948-949 / 1195
29
Table 12. PTM Study: Comparison of LMX and Reference method for Detection of
Listeria monocytogenes
in Food
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
a
MPN = Most Probable Number is based on the POD of reference method test portions across labs using the AOAC MPN calculator, with 95% confidence interval
36
b
N = Number of test portions
37
c
Confirmed positive (confirmed results were identical on OAA and L mono chromogenic plates and OA plates
38
d
X
2
is defined by Mantel-Haenszel as (n-1)(AF-(B+C+D)E)
2
/(A+B+C+D)(A+E)B+C+D+F)(E+F) where n+A+B+C+D+E+F. A X
2
value greater than 3.84 indicates significance at p>0.05.
39
e
Relative Sensitivity rate is defined as the total number of confirmed LMX test positive results divided by the total number of reference method positive test results multiplied by 100
40
Matrix
Strain
MPN
a
/
25g
N
b
VIDAS LMX Method
Reference
Method
Chi Square
d
Relative Sensitivity
e
Presumptive
Pos.
Confirmed
c
Pos.
Positive
Processed cheese
L. monocytogenes
1
< 0.075
5
0
0
0
-
-
0.28
20
5
5
5
0
100
Vanilla ice cream
L. monocytogenes
1
< 0.075
5
0
0
0
-
-
1.02
20
10
10
13
0.78
77
Vanilla ice cream
Independent lab
L. monocytogenes
1
< 0.075
5
0
0
0
-
-
0.90
20
8
8
12
1.56
67
Frozen spinach
L. monocytogenes
4
ScottA
< 0.075
5
0
0
0
-
-
0.28
20
4
4
5
0.206
80
Peanut butter
L. monocytogenes
4a
< 0.075
5
0
0
0
-
-
0.70
20
8
8
10
0.393
80
Cooked shrimp
.
L. monocytogenes
3b
< 0.75
5
0
0
0
-
-
1.1
20
14
14
13
0.074
108
Cooked shrimp
Independent lab
L. monocytogenes
3b
< 0.075
5
0
0
0
-
-
0.42
20
7
7
6
0.11
117
Smoked white
fish
L. monocytogenes
1/2b
< 0.075
5
0
0
0
-
-
1.15
20
8
8
8
0
100
Deli Ham
Independent lab
L. monocytogenes
4b
< 0.075
5
0
0
0
-
-
1.15
20
16
16
14
0.52
114
PTM Certification Report