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VIDAS LMX – Summary 2012 v01
1.5 Background of certification
The VIDAS LMX method was validated with the certificate number BIO 12/27-02/10, on December 2009 for all
human food products (except raw milk cheeses) and environmental samples
Reference protocols :
- EN ISO 16140 : 2003
-
Reference method : EN ISO 11290-1/A1 : 2005 : « Horizontal method for the detection and the
enumeration of
Listeria monocytogenes
. Part 1 : Detection method – Amendment 1 : modification of
isolation media, of haemolysis detection and introduction of fidelity data.
2 Comparative study of methods
2.1 Relative accuracy, relative specificity and relative sensitivity
The aim of the study, according to the reference document EN ISO 16140, is to compare the performances of the
two methods :
-
the reference method EN ISO 11290-1/A1 :2005,
-
the VIDAS LMX method,
on samples naturally contaminated and not contaminated with
Listeria monocytogenes
.
2.1.1 Number and nature of the samples
According to the EN ISO 16140 standard, a minimum of 60 products per category must be analysed, with around
50% of positive products (at least 30 results) and 50% of negative products.
During the initial validation study (December 2009) 323 samples were analysed, and 61 raw milk cheeses during
the extension.
Each category was divided into various types and the results are displayed as follows :
Category
Types
Positive results* Negative results
Total
Meat products
Raw meat
9
11
20
Raw seasoned meat
10
10
20
Delicatessen
11
11
22
Total
30
32
62
Dairy products
Raw milks and pasteurized milk cheeses (cow)
12
5
17
Pasteurized milk cheeses (goat, ewe)
13
13
26
Raw milk cheeses
33
28
61
Desserts, powders of milk
9
12
21
Total
67
58
125
Fish products
Fish fillets and shellfish
13
3
16
Smoked fish
10
24
34
Ready-made meal with fish
8
8
16
Total
31
35
66
Vegetables
Frozen
9
12
21
Raw vegetables (fresh) or 4th range ones
13
13
26
Seasoned
10
14
24
Total
32
39
71
Environment
Various waters
9
10
19
Surface samples
11
9
20
Residues and scraps
10
11
21
Total
30
30
60
TOTAL
190
194
384
*these are positive results by either one or two methods
2.1.2 Artificial contamination of the samples and percentage
Artificial contamination was achieved by using stressed bacterial suspensions, the stress treatment and efficiency
of which have been determined according to EN ISO 16140 and AFNOR validation rules.
80 samples were positive after artificial contamination on a total of 190 positive results of
Listeria monocytogenes.
Overall, 42.1% of positive results were due to artificial contamination.