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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. 4
5
All of the assay steps are performed automatically by the instrument. The 6
reaction medium is cycled in and out of the SPR several times. Part of the 7
enrichment broth is dispensed into the reagent strip. The receptors present will 8
bind to the proteins specific for Listeria receptors, which are coated on the interior 9
of the SPR. Unbound sample components are washed away. Protein conjugated 10
with alkaline phosphatase are cycled in and out of the SPR and will bind to any 11
Listeria receptors which are in turn bound to the specific protein on the SPR wall. 12
. 13
Further wash steps remove unbound conjugate. During the final detection step, 14
the substrate (4-Methylumbelliferyl phosphate) is cycled in and out of the SPR. 15
The conjugate enzyme catalyzes the hydrolysis of this substrate into a fluorescent 16
product (4-Methylumbelliferone), the fluorescence of which is measured at 450 17
nm. 18
19
At the end of the assay, the results are analyzed automatically by the instrument 20
which generates a test value for each sample. This value is compared to a set of 21
stored standards (thresholds) and each result is interpreted (positive, negative). 22
23
1.3 Summary of the LMX PTM/Precollaborative Study 24
25
The VIDAS LMX method was validated according to AOAC Guidelines (2002) 26
in a harmonized PTM study. The aim of this study was to demonstrate that the 27
VIDAS LMX method could detect L. monocytogenes in a variety of foods as 28
claimed by the manufacturer. 29
30
In the PTM study, there were 7 matrices tested using a 26-hr proprietary 31
enrichment broth protocol for the VIDAS LMX method and the appropriate 32
reference method: deli-ham (USDA/FSIS ML , processed cheese (AOA , 33
vanilla ice cream (AOAC), cooked shrimp (FDA-BA , smoked white fish 34
(FDA-BAM), frozen spinach (FDA-BAM) and peanut butter (FDA-BAM). 35
Additionally, there were five ready-to-eat matrices (hot dogs, deli turkey, deli 36
ham, fermented sausage, and liver paté) evaluated using the VIDAS LMX 37
method, the Health Canada MFHPB-3 method and the USDA/FSIS MLG 38
method. 39
40
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
4 Health Canada MFHPB-30,
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