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VIDAS LMX & LPT Collaborative Study
April 19, 2013
OMA-2013-Apr-XXX
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INTRODUCTION
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The goal of this collaborative study is to estimate the following performance
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parameters of the VIDAS®
L. monocytogenes
Xpress (LMX) and the VIDAS® UP
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Listeria
(LPT) assays: probability of detection (POD) and the difference in the POD
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at 3 contamination levels for both the candidate and reference methods. Test
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portions from 3 different contamination levels, including negative controls, will be
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sent to collaborators where they will perform the VIDAS LMX and LPT methods
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along with the corresponding reference method. Soft Mexican cheese will be tested
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at 25g using the supplemented LMX broth and the VIDAS LMX method, at 25g
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using the LPT broth and the VIDAS LPT method and at 125g using the LPT broth
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and both the VIDAS LMX and LPT methods.
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1.1
Description of the VIDAS LMX Method
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VIDAS® LMX test is an enzyme immunoassay for use on the automated
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VIDAS® system for the detection of
Listeria monocytogenes
using the Enzyme
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Linked Fluorescent Assay (ELFA) method.
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The Solid Phase Receptacle (SPR®) serves as the solid phase as well as the
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pipetting device. The interior of the SPR® is coated with anti-
L. monocytogenes
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antibodies adsorbed on its surface. Reagents for the assay are ready-to-use and
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pre-dispensed in the sealed reagent strips.
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The VIDAS instrument performs all of the assay steps automatically. An aliquot
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of the enrichment broth is dispensed into the reagent strip. The reaction medium
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is cycled in and out of the SPR® several times. Target antigens present will bind
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to the anti-
Listeria monocytogenes
antibodies, which are coated on the interior of
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the SPR®. Unbound sample components are washed away. The detector
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antibody conjugate is cycled in and out of the SPR® and will bind to any
L.
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monocytogenes
antigens which are bound to the antibodies on the SPR® wall.
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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
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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 or negative).
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1.2
Description of the VIDAS LPT Method
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VIDAS® LPT test is an enzyme immunoassay for use on the automated VIDAS®
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system for the detection of
Listeria
antigens using the ELFA method. The assay
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also incorporates phage proteins allowing an increase in sensitivity and specificity
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DRAFT DOCUMENT
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