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potentially infectious and handled observing the usual safety precautions (do not
1
ingest or inhale)
2
3
Inclusivity Study
4
Methodology
5
The purpose of inclusivity testing is to ensure that the VIDAS LPTtest can detect a
6
representative range of
Listeria
. All cultures used for inclusivity testing were checked for
7
purity prior to testing. Fifty
Listeria
strains (25
L. Monocytogenes
and 25 other
Listeria
8
species)
were enriched in LPT broth for 26h at 30°C and tested on the VIDAS LPT assay.
9
10
Results
11
The inclusivity results are presented in Table 1. All
Listeria
strains tested were detected by the
12
VIDAS LPT assay.
13
14
Exclusivity study
15
Methodology
16
The purpose of exclusivity testing is to determine the ability of the LPT method to
17
discriminate target organisms from non-target organisms. Thirty non-
Listeria
strains were
18
cultivated in TSB+YE broth for 26h at 37°C and then tested using the VIDAS LPT assay.
19
Results
20
The exclusivity results are presented in Table 2. The thirty non-
Listeria
strains tested
21
were negative by the VIDAS LPT assay.
22
Method Comparison Study - Foods
23
This precollaborative study was conducted with reference to AOAC guidelines (6)
24
outlined in the AOAC General Referee approved harmonized PTM/OMA protocol. The
25
method comparison study consisted of evaluation of the LPT compared to various
26
reference methods depending on the food type. Seven foods (deli ham, pepperoni, beef
27
hot dogs, chicken nuggets, chicken liver paté, ground beef, deli turkey) as well as 4
28
environmental surfaces (plastic, stainless steel, ceramic and concrete) were tested at
29
contract laboratories comparing the LPT method and the USDA/FSIS MLG method.
30
Dairy foods (vanilla ice cream and soft cheese were tested by both the AOAC method
31
(993.12) and the LPT method. Six other foods (cooked shrimp, smoked salmon,
32
cantaloupe, bagged mixed salad, peanut butter and black pepper were tested by the LPT
33
method and compared to the FDA-BAM method. A background screen of each food was
34
conducted prior to inoculation and natural contamination of
Listeria
was not detected for
35
any food. A total plate count was also performed on each food to determine the
36
microbial load. Within each sample set there were 5 uninoculated samples and 20 low-
37
level inoculated samples for each method. The target levels of the organism used for
38
challenging each food matrix was as follows: 0.2-2 colony forming units (cfu)/25g of
39
46