The preferred standard methodology, and permitted alternative rapid methodologies, to be used for detection and isolation of Listeria monocytogenes are as follows. Presumptive contaminated food lots are sampled. Generally, sub-samples are composited if required by FDA field laboratory instructions. Analytical portions (25 g) are pre-enriched for Listeria species at 30° C for 4 h in buffered Listeria enrichment broth (BLEB), equivalent (26) to AOAC/IDF dairy products enrichment broth (4, 40) base containing sodium pyruvate (43). At the fourth hour of the incubation, the selective agents (acriflavin, 10 mg/L (4, 40); sodium nalidixate, 40 mg/L; optional antifungal, e.g. cycloheximide 50 mg/L) are added. Incubation for selective enrichment is continued at 30° C for a total of 48 h. The enrichment culture is streaked at 24 and 48 h on one of the prescribed differential selective-agars in order to isolate Listeria species.