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VIDAS LMX – Summary 2012 v01
5 General conclusion
The validation study of the methods was conducted according to the reference document EN ISO 16 140 (2003).
The
comparative study
allows assessing :
-
the relative accuracy, the relative sensitivity and the relative specificity,
-
the relative detection level,
-
the inclusivity and the exclusivity.
-
The performances of the VIDAS LMX method were compared with those in the reference method EN ISO 11290-
1/A1: 2005 by the analysis of 384 samples distributed in five categories of products.
The relative accuracy obtained according to the procedures of confirmations was 90.4 %, the relative sensitivity
89.5 % and the relative specificity 91.1 %, according to the calculations required by the EN ISO 16140 standard.
Because the positive samples by the alternative method are positive confirmed samples, the sensitivities were
recalculated relative to all positive results according to the calculations recommended by the AFNOR and are of
90.5 % for the alternative method and 90.0 % for the reference method.
The total number of discordances was 37 : 18 false negative results and 19 additional positive results.
In final, both methods were considered as statistically equivalent.
The relative level of detection of the VIDAS LMX method and of the reference method was evaluated by artificial
contaminations of six different products, representative of five categories tested.
It was between 0.2 and 1.8 cells per 25 g for alternative method and between 0.2 and 1.3 cells per 25 g for the
reference method.
The specificity of the method is good since all the strains of
Listeria monocytogenes
were detected (inclusivity) and
no cross reaction was observed when other strains were tested with complete protocol of the alternative method
(exclusivity).
The
interlaboratory study
results obtained for all of the 11 selected laboratories show that the alternative method
and the reference method have comparable values of relative accuracy, specificity and sensitivity and are of the
same order as those obtained during the preliminary study.
The variability of the alternative method (accordance, concordance, Odds ratio) is comparable with the variability of
the reference method.
Set of results led to
AFNOR VALIDATION certification
according to EN ISO 16140, of the VIDAS LMX method
(certificate n°BIO 12/27 – 02/10), for the detectio n of
Listeria monocytogenes
in all human food products (including
raw milk cheeses) and environmental samples.
Lille, November 22th 2012
Mélinda Maux
Technical manager