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3M MDA 2
Listeria
species and
L. monocytogenes
Collaborative Study
OMA-2016-MONTH-XXX
5/4/16
3.0
Test Portion Preparation
3.1
Preparation of inoculum
. Deli turkey should be inoculated with heat-stressed
organisms (e.g. 50°C for 10 min). The degree of injury caused by heat-stressing
should be demonstrated by plating the inoculum in triplicate on selective and non-
selective agars. The degree of injury is calculated as:
100 )
1(
x
n
n
nonselect
select
−
where
n
select
= mean number of colonies on selective agar and
n
nonselect
= mean
number of colonies on nonselective agar. Raw chicken breast should be
inoculated with a fresh, overnight culture diluted to the appropriate concentration.
3.2
Products will be obtained from local retail outlets. All food types will be screened
for the presence of
Listeria
using the reference method. Any lots that screen
positive will be confirmed out to the species level as per the specified reference
method for that food type. Naturally contaminated test portions will be used if
available at sufficient levels. Alternatively, the test portions will be artificially
inoculated to meet the targets of 0.2-2.0 cfu/test portion for the low and 2 – 5
cfu/test portion for the high with the appropriate concentration of a wet inoculum.
3.3
Preparation of test portions.
Each food type will be chopped into small pieces
or divided and a liquid inoculum will be added drop-wise to a bulk quantity of
food for each inoculation level. The bulk quantity will then be mixed to achieve
equal distribution of analyte throughout. The test portions will be stored at 2-8
°
C
for 48-72 h prior to testing.
3.4
Shipment of test portions.
Test portions will be packaged in leak-proof,
insulated containers and shipped (according to the Dangerous Goods Regulations
IATA for Infections Substances) refrigerated via overnight courier to the
collaborators to arrive on a Friday. Test portion processing and analysis will
begin on Monday
.
All refrigerated test portions will be packed with ice packs to
maintain a temperature of <7
°
C during transport. A temperature control sample
will be included with each shipment to verify temperature of sample upon receipt.
Upon arrival, the test portions will be stored at 2-8
°
C until they are analyzed.
3.5
Microbiological analysis.
Each collaborator will receive36 x 60g raw chicken
breast test portions (to be divided) and 72 x 125g deli turkey test portions. They
will be instructed to weigh 25g raw chicken breast for the 3MMDA2 methods and
another 25g for the reference methods. For deli turkey, they will be instructed to
test one 125g test portion for the 3M MDA2 -
Listeria monocytogenes
method and
the other 125g test portion for the USDA/FSIS MLG 8.09 reference method. All
test portions assayed by the 3M MDA2methods will be confirmed following the
reference method for confirmation of
Listeria monocytogenes
. The reference
method confirmation procedures following the USDA/FSIS MLG 8.09 should be
AOAC Research Institute
Expert Review Panel Use Only
OMAMAN-29/OMAMAN-30 Combined Collaborative Study Protocol
OMA ERP - June 2016
ERP Use Only