The identification of Listeria species

The purpose of this study was to compare methods for the identification of Listeria species. Three hundred and fifty cultures representing the six species of Listeria were tested using conventional sugar fermentation and haemolytic reactions, as well as the hydrolysis of the dl-alanine β-naphthylamide (DLABN), and the API Listeria identification test kit. Using conventional tests, 99% of cultures were correctly identified: four L. monocytogenes were misidentified as L. innocua. The DLABN hydrolysis test distinguished L. monocytogenes from the remainder of the genus for 98% of the cultures: 6 out of 14 L. ivanovii isolates gave atypical results. There was correct identification for 97% of the cultures using the API Listeria test kit and no misidentifications were obtained: nine cultures (six L. monocytogenes and three L. innocua) gave equivocal profiles which were not ascribed to any species.