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Comparative Evaluation of the VIDAS®UP Listeria (LPT) for the
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Detection
Listeria
speciesin a Variety of Foods and Environmental Surfaces
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Abstract
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VIDAS®UP (LPT test) is a newly developed assay for use on the automated VIDAS®
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system for the detection of
Listeria
antigens using the Enzyme Linked Fluorescent Assay
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(ELFA) method. This assay incorporates phage proteins to increase the sensitivity and
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specificity compared to traditional immunoassays. This precollaborative study was
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conducted as part of the AOAC Official Methods validation process. Fifteen different
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foods (deli ham, pepperoni, beef hot dogs, chicken nuggets, chicken liver paté, ground
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beef, deli turkey, cooked shrimp, smoked salmon, cantaloupe melon, bagged mixed salad,
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peanut butter, black pepper, vanilla ice cream, queso cheese) and four environmental
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surfaces (plastic, stainless steel, ceramic and concrete) were tested at two contract
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laboratories. For each matrix five uninoculated samples and twenty low-level inoculated
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samples were tested by the LPT and appropriate reference methods. The target levels of
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the organism used for challenging each matrix was 0.2-2 colony forming units (cfu)/test
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portion or surface swab for the low level inoculation and 0 cfu/25 g for the uninoculated
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control samples. The aim was to achieve fractional positive data within the range 5-15
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positives for the low inoculation level. The results of this study demonstrate that the
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VIDAS
®
LPT method was equivalent to or better than the reference methods for the
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detection of
Listeria
species. The VIDAS
®
LPT method has a simple one-step
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enrichment procedure for 25g test samples and offers a significant savings in time when
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compared to cultural methods or other immunoassays by giving presumptive results in
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less than 28 hours for foods and less than 24h for environmental surfaces. Samples were
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also validated using 125 g test portions enriched in primary and secondary LPT
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enrichment broth. The LPT test method was determined to be equivalent to the reference
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methods for the detection of
Listeria
species in 125g test portions of ground beef, deli
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ham and turkey and Mexican style soft-cheese (queso fresco). In addition, confirmation
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using direct plating of LPT broth on ALOA showed exact agreement with the traditional
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plating media.
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Method Authors
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Ron Johnson
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bioMérieux, Inc.
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595 Anglum Drive
35
Hazelwood, MO 63042
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USA
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