The efficacy of confirmatory tests recommended by a PrPN EN ISO 11290-1:1999 standard for identification of Listeria spp. and L. monocytogenes strains in food products was examined in our studies. Confirmatory assays consisted of catalase and motility (a characteristic 'umbrella- -shape' outgrowth) tests for Listeria spp. as well as hemolytic activity and sugar fermentation (D-xylose and L-rhamnose) tests for L. monocytogenes. They were compared with results of multiplex PCR (polymerase chain reaction) designed for confirmation of genus and species. Seventy strains were tested. In the great majority (52 strains, 74.3%) they were of beef and pork carcasses origin. Eighteen strains (25.7%) were collected by swabbing in meat-processing environment. All presumptive strains were motile in ambient temperature, catalase-positive, presented hemolytic activity and characteristic morphological features, which enabled to classify them as L. monocytogenes. The comparison of pathogen identification results carried out with the standard tests and genetic analysis revealed that 84.3% of results was conformable (45 strains recognized as L. monocytogenes and 14 strains identified as Listeria spp. using both procedures). Variations referred to over 15% of results. Nine strains (12.9%) were identified as L. monocytogenes based on the sugar fermentation pattern whereas not confirmed by multiplex PCR. The affiliation of two strains (2.8%) identified as L. monocytogenes by multiplex PCR was not confirmed in the sugar fermentation test. The number of inaccurately classified strains in tests recommended by ISO standard highlights its limited efficacy for identification of L. monocytogenes strains.
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