Abstract niet beschikbaarA trial with 42 laboratories participating, was organized in May 1990 to test the L.monocytogenes reference materials in combination with reference materials containing competitive microorganisms. The materials were tested by 2 methods, one standardized for all laboratories (SM method) and the other method chosen by the laboratories themselves (OWN method). Thirty samples were tested by each method of which nine were negative for Listeria. The contamination level of the L.monocytogenes capsules was 4.9 cfu/capsule. Each laboratory was expected to find the organism in 18 or more out of the 21 L.monocytogens contaminated samples. The total contamination of microorganisms was 2.9 x 10-4 cfu/capsule. Using the standard method Listeria monocytogenes was detected in 79.3% of the contaminated samples, and 45% of the participating laboratories made the expected number of isolations. With the OWN method these percentages were 78.1% and 52.5% respectively. Concluded was that the materials tested are suitable to test the performance of the detection method for Listeria in a laboratory.EG/BCR
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