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VIDAS LMX & LPT Collaborative Study
April 19, 2013
OMA-2013-Apr-XXX
3.3
Study Schedule
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3.3.1
The study will take place over approximately 4 weeks. Data should be
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sent to the study director by the end of the fourth week.
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3.3.2
The contract laboratory will prepare the test portions and ship the test
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portions refrigerated via overnight courier to the collaborators to arrive on
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a Friday. Test portion processing and analysis will begin on Monday.
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Data forms will be completed and faxed or emailed back to the co-Study
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Director by the following Friday.
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4.0
Test Portion Preparation
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4.1
Soft Mexican cheese will be obtained from local retail outlets and screened using
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both the VIDAS and reference methods for the presence of
L. monocytogenes
.
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Naturally contaminated test portions will be used if available at sufficient levels.
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Alternatively, the test portions will be artificially inoculated to meet the targets of
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0.2-2.0 cfu/test portion for the low and 2 – 5 cfu/test portion for the high with the
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appropriate concentration of a wet inoculum.
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4.2
Preparation of test portions.
A liquid inoculum (heat-stressed, e.g. 50ºC for 10
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min) will be added drop-wise to a bulk quantity of food for each inoculation level.
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The bulk quantity will then be mixed to achieve equal distribution of analyte
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throughout. The test portions will be stored at 2-8
°
C for 72-96 h prior to testing.
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4.2.1
The degree of injury will be estimated as
100 )
1(
x
n
n
nonselect
select
−
, where n
select
=
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number of colonies on selective agar and n
nonselect
= number of colonies on
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non-selective agar. The heat stress must achieve 50 – 80% injury of the
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inoculum and be recorded in the final report.
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4.3
Shipment of test portions.
Test portions will be packaged in leak-proof,
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insulated containers and shipped (according to the Dangerous Goods Regulations
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IATA for Infections Substances) by overnight carrier to arrive the day before
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initiation of analysis
.
All refrigerated test portions will be packed with ice packs
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to maintain a temperature of <7
°
C during transport. A temperature control sample
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will be included with each shipment to verify temperature of sample upon receipt.
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Upon arrival, the test portions will be stored at 2-8
°
C until they are analyzed.
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4.4
Microbiological analysis.
The test portion enrichment broth is different for the
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VIDAS and reference method. Therefore, each collaborator will receive a
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separate test portion for each method.
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Week 1 - Collaborators will be instructed to enrich the 25g VIDAS test portions
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in supplemented LMX broth followed by the VIDAS LMX test kit. Another 25g
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test portion will be tested using the AOAC reference method.
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DRAFT DOCUMENT
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