For selective and differential isolation of Listeria monocytogenes .
ALOA LISTERIA AGAR BASE is used for selective and differential isolation of Listeria monocytogenes. This Agar Listeria medium is recommended according to Ottaviani & Agosti (ALOA), complete with selective and enrichment supplements. Casein enzymatic hydrolysate, Peptic digest of animal tissue and Yeast extract provide nitrogen, vitamins and minerals. Sodium chloride maintains the osmotic balance of the medium. Phosphates provide buffering capacity. The selectivity of the medium is due to lithium chloride and antimicrobial selective mixture containing Cephtazidime, Polymyxin B, Nalidixic acid and Cycloheximide. The differential activity is due to the presence in the medium of the chromogenic compound X-glucoside as a substrate for the detection of β-glucosidase enzyme, common to all Listeria species. Differentiation of Listeria monocytogenes from other Listeria species is based on phosphatidylinositolspecific phospholipase C (PIPLC) activity. Phospholipase C enzyme hydrolyses the purified substrate (TS 229) added to the medium resulting in an opaque halo around Listeria monocytogenes colonies. On combining of both substrates, it is possible to differentiate the colonies of Listeria spp., which grow with a green-blue colour, from the colonies of L. monocytogenes, surrounded by an opaque halo. Agar Listeria acc. to Ottaviani & Agosti (ALOA) allows differentiating L. monocytogenes even in presence of a mixed flora, after incubation of 24 +/- 2 hours in an easy and reliable way, as well as direct streaking, or after enrichment in the usual selective liquid media.