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2
Listeriamonocytogenes
is ubiquitous in the environment, often found in soil, water, sewage and
1
damp environments, making it difficult to control in the food processing environment [1]. The
2
organism’s ability to survive in processing facilities has led to some highly publicized recent
3
outbreaks, specifically in ice cream and packaged salads [3]. The 3M
™
Molecular Detection
4
Assay(MDA) 2 -
Listeria monocytogenes
method,usinga combination of bioluminescence and
5
isothermal amplification of nucleic acid sequences,allows for the rapid and specific detection of
6
Listeria monocytogenes
in a broad range of food types and environmental surfaces after 24 to
7
2832
hoursof pre-enrichment. After enrichment, samples are evaluated using the 3M MDA 2 -
8
Listeria monocytogenes
on the 3M
™
Molecular Detection System (MDS).Presumptive positive
9
results are reported in real-time while negative results are displayed after completion of the assay
10
in approximately 75 minutes.
11
Prior to the collaborative study, the 3M MDA 2 -
Listeria monocytogenes
method was validated
12
according to AOAC Guidelines[4] in a harmonized AOAC
®
Performance Tested Method
SM
13
(PTM) study. The objective of the PTM study was to demonstrate that the 3M MDA 2-
Listeria
14
monocytogenes
method could detect
Listeria monocytogenes
in a broad range of food matrices
15
and environmental surfaces as claimed by the manufacturer. For the 3M MDA 2
- Listeria
16
monocytogenes
PTM evaluation, 13 matrices were evaluated:hot dogs (25g & 125g), salmon
17
(25g), deli turkey (25g & 125g), cottage cheese (25g), chocolate milk (25 mL), vanilla ice cream
18
(25g), queso fresco (25g), romaine lettuce (25g), melon (whole), raw chicken leg pieces (25g);
19
concrete (sponge, 225 mL & 100 mL), stainless steel (sponge, 225 mL), and plastic
20
(Enviro
sS
wab, 10 mL) environmental samples.
21
Additional PTM parameters (inclusivity, exclusivity, ruggedness, stability and lot-to-lot
22
variability) tested in the PTM studies satisfied the performance requirements for PTM approval.
23
The method was awarded PTM certification number 081501 on August 18
th
, 2015.
24
The purpose of this collaborative studywas to compare the reproducibility of the 3M MDA 2 -
25
Listeria monocytogenes
method to the United States Department of Agriculture (USDA) Food
26
Safety Inspection Service (FSIS) -Microbiology Laboratory Guidebook (MLG)Chapter 8.09
27
Isolation and Identification of Listeria monocytogenes from Red Meat, Poultry and Egg
28
Products, and Environmental Samples
[5] for deli turkey (125 g) and raw chicken breast fillet.
29
30
Collaborative Study
31
32
Study Design
33
34
In this collaborative study, two matrices,deli turkeyand raw chicken breast fillet,
35
wereevaluated.The matrices were obtained from a local retailer and screened for the presenceof
36
Listeria monocytogenes
by the USDA/FSIS MLG 8.09 reference method
.
The raw chicken breast
37
fillet was artificially contaminated with fresh unstressed cells of
Listeria monocytogenes
,
38
American Type Culture Collection (ATCC) 7644, and the deli turkeywas artificially
39
contaminated with heat stressed cells
(Table 2)
of
Listeria monocytogenes
,ATCC 19115,at two
40
inoculation levels: a high inoculation level of approximately 2-5 colony-forming units (CFU)/test
41
portion and a low inoculation level of approximately 0.2-2 CFU/test portion. A set of un-
42
inoculated control test portions (0 CFU/test portion) were also included.
43
Twelve replicate samples from each of the three inoculation levels were analyzed by each
44
method. Two sets of samples (72 total) were sent to each laboratory for analysis by 3M MDA 2 -
45
Listeria monocytogenes
and the USDA/FSIS MLG Chapter 8.09 reference method due to the
46
different sample enrichment procedures for each method. Additionally, collaborators were sent a
47
60 g test portion and instructed to conduct atotal aerobic plate count (APC) using 3M
™
48