Mode of Action
The nutrient substrates contained in the L-PALCAM Broth enable a very good proliferation of Listeria. Growth of the undesirable accompanying flora is inhibited by the selective substances Polymyxin-B-sulfate, acriflavine, lithium chloride and ceftazidime. Soybean lecithin has properties similar to egg-yolk emulsion, meaning that additional supplementation with eggyolk emulsion is not required. Esculin, ammonium iron(III) citrate, mannitol, and phenol red enable a differential-diagnostic statement regarding the possible presence of Listeria.
Listeria hydrolyse the glucoside esculin into glucose and esculetin. The latter substance reacts with iron(III) ions to form an olive-green to black complex.
When Listeria proliferate in the L-PALCAM Broth, therefore, in the majority of cases the broth turns black-brown in colour.
Typical Composition (g/litre)
Peptone 23.0; yeast extract 5.0; lithium chloride 10.0; esculin 0.8; ammonium iron(III) citrate 0.5; D(-)mannitol 5.0; phenol red 0.08; soybean lecithin 1.0; Tween® 80 2.0.
Suspend 23.7 g in 500 ml of demin. water, autoclave (15 min at 121 °C). Suspend the contents of 1 vial of PALCAM Listeria Selective Supplement acc. to VAN NETTEN et al. in 1 ml sterile, distilled water and add to the basic broth, which has been cooled below 50 °C. Carefully swirl to mix the selective supplement into
the broth homogeneously.
pH: 7.4 ± 0.2 at 25 °C.
The prepared broth (incl. supplement) is opalescent/turbid and red
Experimental Procedure and Evaluation
Inoculate the broth with sample material (generally 25 g sample material into 225 ml broth) and incubate at 30 °C for 24-48 hours aerobically.
Approximately 0.1 ml of the broth is then smeared on the surface of a Listeria selective agar (e.g. PALCAM Agar or Oxford Agar) in a way to obtain well isolated single colonies.