AGAR-BASED 24-H METHOD FOR PRESUMPTIVE IDENTIFICATION OF LISTERIA-MONOCYTOGENES

A rapid system for the presumptive identification of Listeria monocytogenes was developed using agar-based media in place of conventional liquid media. The system allows determination of oxidase, catalase, rhamnose and xylose fermentation, and CAMP reaction within 24 h. A single four-section compartmented petri dish was prepared containing purple agar base with xylose, purple agar base with rhamnose, trypticase soy agar with yeast extract (TSA/YE), and TSA/YE with 5% sheep blood. All four media and a 10-ml portion of brain heart infusion broth, to examine motility, were inoculated simultaneously from a single colony for presumptive identification. A 100% correlation between conventional procedures requiring 7 d and the rapid system was demonstrated on 935 L. monocytogenes cultures isolated from food and food plants. The rapid screening test was also useful in differentiating other Listeria spp.