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VIDAS LMX & LPT Collaborative Study
April 19, 2013
OMA-2013-Apr-XXX
Week 2 - Collaborators will be instructed to enrich the 25g VIDAS test portions
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in LPT broth followed by the VIDAS LPT test kit. Another 25g test portion will
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be tested using the AOAC reference method.
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Week 3 - Collaborators will be instructed to enrich the 125g VIDAS test portions
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in LPT broth followed by a 1.0 mL transfer into 10 mL LPT broth. The
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secondary enrichment will then be tested by both the VIDAS LMX and LPT test
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kits. A 25g test portion will be tested using the AOAC reference method.
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All test portions assayed by the VIDAS method will be confirmed following the
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reference method as well as a chromogenic agar, ALOA, for confirmation of
L.
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monocytogenes
species. Typical colonies will be identified by the VITEK2 GP or
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API Listeria.
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One additional control (negative) test portion will be provided to each
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collaborator for each matrix to determine the total plate count on the day of
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analysis.
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4.5
Most Probable Number (MPN) Analysis.
To determine the level of
L.
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monocytogenes
in the inoculated food test portions. On the day that the analysis
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of the test samples is initiated, a 5-tube 3-level Most Probably Number (MPN)
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estimation of contamination levels will be conducted by the coordinating
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laboratory using the AOAC reference method. The MPN analysis scheme may
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also make use of the reference method replicates (see
Appendix X-A
of the AOAC
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Guidelines for details). To each test portion, add selective enrichment broth
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(AOAC enrichment) to make a 1:10 dilution. Follow the reference method
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through to confirmations. Use the number of positives from the high, medium
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and low levels to calculate the MPN for each inoculated level of each matrix.
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Access the MPN calculator
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( http://www.lcfltd.com/customer/LCFMPNCalculator.exe )to determine the MPN
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values and 95% confidence intervals. Data should be entered from high level to
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low. Report MPN as MPN/test portion.
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5.0
VIDAS®
L. monocytogenes
Xpress (LMX) Method
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5.1
Applicability
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For the detection of
L. monocytogenes
species in a Variety of Foods.
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Caution
:
Listeria monocytogenes
is of particular concern for pregnant
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women, the aged and the infirmed. It is recommended that these
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concerned groups avoid handling this organism. Dispose of all
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reagents and other contaminated materials by acceptable procedures for
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potentially biohazardous materials.
Some reagents in the kit contain 1
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g/L concentrations of sodium azide. Check local regulations prior to
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DRAFT DOCUMENT
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