216 / 596
2
Assay(MDA) 2 -
Listeria monocytogenes
method,usinga combination of bioluminescence and
1
isothermal amplification of nucleic acid sequences,allows for the rapid and specific detection of
2
Listeria monocytogenes
in a broad range of food types and environmental surfaces after 24 to 28
3
hoursof pre-enrichment. After enrichment, samples are evaluated using the 3M MDA 2 -
4
Listeria monocytogenes
on the 3M
™
Molecular Detection System (MDS). Presumptive positive
5
results are reported in real-time while negative results are displayed after completion of the assay
6
in approximately 75 minutes.
7
Prior to the collaborative study, the 3M MDA 2 -
Listeria monocytogenes
method was validated
8
according to AOAC Guidelines[4] in a harmonized AOAC
®
Performance Tested Method
SM
9
(PTM) study. The objective of the PTM study was to demonstrate that the 3M MDA 2-
Listeria
10
monocytogenes
method could detect
Listeria monocytogenes
in a broad range of food matrices
11
and environmental surfaces as claimed by the manufacturer. For the 3M MDA 2
- Listeria
12
monocytogenes
PTM evaluation, 13 matrices were evaluated:hot dogs (25g & 125g), salmon
13
(25g), deli turkey (25g & 125g), cottage cheese (25g), chocolate milk (25 mL), vanilla ice cream
14
(25g), queso fresco (25g), romaine lettuce (25g), melon (whole), raw chicken leg pieces (25g);
15
concrete (sponge, 225 mL & 100 mL), stainless steel (sponge, 225 mL), and plastic (Enviroswab,
16
10 mL) environmental samples.
17
Additional PTM parameters (inclusivity, exclusivity, ruggedness, stability and lot-to-lot
18
variability) tested in the PTM studies satisfied the performance requirements for PTM approval.
19
The method was awarded PTM certification number 081501 on August 18
th
, 2015.
20
The purpose of this collaborative studywas to compare the reproducibility of the 3M MDA 2 -
21
Listeria monocytogenes
method to the United States Department of Agriculture (USDA) Food
22
Safety Inspection Service (FSIS) -Microbiology Laboratory Guidebook (MLG)Chapter 8.09
23
Isolation and Identification of Listeria monocytogenes from Red Meat, Poultry and Egg
24
Products, and Environmental Samples
[5] for deli turkey (125 g) and raw chicken breast fillet.
25
26
Collaborative Study
27
28
Study Design
29
30
In this collaborative study, two matrices,deli turkeyand raw chicken breast fillet, wereevaluated.
31
The matrices were obtained from a local retailer and screened for the presenceof
Listeria
32
monocytogenes
by the USDA/FSIS MLG 8.09 reference method
.
The raw chicken breast fillet
33
was artificially contaminated with fresh unstressed cells of
Listeria monocytogenes
, American
34
Type Culture Collection (ATCC) 7644, and the deli turkeywas artificially contaminated with
35
heat stressed cells of
Listeria monocytogenes
,ATCC 19115,at two inoculation levels: a high
36
inoculation level of approximately 2-5 colony-forming units (CFU)/test portion and a low
37
inoculation level of approximately 0.2-2 CFU/test portion. A set of un-inoculated control test
38
portions (0 CFU/test portion) were also included.
39
Twelve replicate samples from each of the three inoculation levels were analyzed by each
40
method. Two sets of samples (72 total) were sent to each laboratory for analysis by 3M MDA 2 -
41
Listeria monocytogenes
and the USDA/FSIS MLG Chapter 8.09 reference method due to the
42
different sample enrichment procedures for each method. Additionally, collaborators were sent a
43
60 g test portion and instructed to conduct atotal aerobic plate count (APC) using 3M
™
44
Petrifilm™Rapid Aerobic Count Plate (AOAC Official Method 2015.13) [6] on the day samples
45
were received for the purpose of determining the total aerobic microbial load.
46
A detailed collaborative study packet outlining all necessary information related to the study
47
including media preparation, test portion preparation and documentation of results was sent to
48
each collaborating laboratory prior to the initiation of the study. A conference call was then
49
AOAC Research Institute
E pert Review Panel Use Only
OMAMAN-30 A/ Collaborative Study Manuscript
OMA ERP June 2016
ERP Use Only