VIDAS LMX & LPT Collaborative Study
April 19, 2013
OMA-2013-Apr-XXX
compared to traditional immunoassays. The SPR serves as the solid phase as well
1
as the pipetting device. The interior of the SPR is coated with proteins specific
2
for
Listeria
receptors adsorbed on its surface. Reagents for the assay are ready-to-
3
use and pre-dispensed in the sealed reagent strips.
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All of the assay steps are performed automatically by the instrument. The
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reaction medium is cycled in and out of the SPR several times. Part of the
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enrichment broth is dispensed into the reagent strip. The receptors present will
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bind to the proteins specific for
Listeria
receptors, which are coated on the interior
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of the SPR. Unbound sample components are washed away. Protein conjugated
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with alkaline phosphatase are cycled in and out of the SPR and will bind to any
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Listeria
receptors which are in turn bound to the specific protein on the SPR wall.
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.
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Further wash steps remove unbound conjugate. During the final detection step,
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the substrate (4-Methylumbelliferyl phosphate) is cycled in and out of the SPR.
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The conjugate enzyme catalyzes the hydrolysis of this substrate into a fluorescent
16
product (4-Methylumbelliferone), the fluorescence of which is measured at 450
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nm.
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At the end of the assay, the results are analyzed automatically by the instrument
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which generates a test value for each sample. This value is compared to a set of
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stored standards (thresholds) and each result is interpreted (positive, negative).
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1.3
Summary of the LMX PTM/Precollaborative Study
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The VIDAS LMX method was validated according to AOAC Guidelines (2002)
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in a harmonized PTM study. The aim of this study was to demonstrate that the
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VIDAS LMX method could detect
L. monocytogenes
in a variety of foods as
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claimed by the manufacturer.
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In the PTM study, there were 7 matrices tested using a 26-hr proprietary
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enrichment broth protocol for the VIDAS LMX method and the appropriate
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reference method: deli-ham (USDA/FSIS ML
G 1 ), processed cheese (AOA
C 2 ),
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vanilla ice cream (AOAC), cooked shrimp (FDA-BA
M 3 ), smoked white fish
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(FDA-BAM), frozen spinach (FDA-BAM) and peanut butter (FDA-BAM).
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Additionally, there were five ready-to-eat matrices (hot dogs, deli turkey, deli
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ham, fermented sausage, and liver paté) evaluated using the VIDAS LMX
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method, the Health Canada MFHPB-3
0 4method and the USDA/FSIS MLG
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method.
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1
USDA/FSIS Microbiological Laboratory Guidebook, 8.07, August 2, 2009 effective date
2
AOAC 993.12
3
FDA Bacteriological Analytical Manual, Chapter 10, January 2003 version
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Health Canada MFHPB-30,
http://www.hc-sc.gc.ca/fn-an/res-rech/analy-meth/microbio/volume2/mfhpb30-eng.php
DRAFT DOCUMENT
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