LISTERIA OXFORD AGAR BASE W/ 1.2% AGAR

Description

The genus Listeria contains six species; L. monocytogenes, L. innocua, L. seeligeri, L. welshimeri, L. ivanovii, and L. grayi. Listeria monocytogenes is the only species of the genus Listeria that is important as a human pathogen. The universal occurrence of L. monocytogenes in food and the risk of contracting food-borne L. monocytogenes listeriosis has been thoroughly reviewed recently and L.monocytogenes has been detected in the food processing environment, such as on food contact surfaces and equipment. Other species; Listeria seeligeri, Listeria welshimeri and Listeria ivanovii have been related with animal diseases. L. ivanovii and L. monocytogenes are pathogenic for mice and other animals. However, only L. monocytogenes is commonly associated with human listeriosis. Listeriosis associated infection by L. ivanovii, and even L. seeligeri is extremely rare in humans. 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 to AOAC/IDF dairy products enrichment broth base containing sodium pyruvate. At the fourth hour of the incubation, the selective agents (acriflavin, 10 mg/ L; 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. The selective and differential media containing esculin and ferric citrate aids in Listeria isolation and detection based on esculin hydrolysis. Listeria Oxford Medium Base is based on the formulation described by Curtis et al for the selective isolation of L. monocytogenes from food specimens, and is recommended by FDA BAM for the same purpose.