Chromogenic listeria agar plate shows all listeria species, as clearly visible blue/green colonies with listeria monocytogenes colonies showing a distinctive opaque white halo
Oxoid has launched a new chromogenic medium for the improved isolation, enumeration and identification of listeria from food samples.
In addition to providing presumptive identification of listeria species, Oxoid Chromogenic Listeria Agar (OCLA) plate (code PO5165A) is also able to differentiate pathogenic listeria monocytogenes and listeria ivanovii from other listeria species. The X-glucoside chromogen within the medium is cleaved by the enzyme b-glucosidase, common to all listeria species, resulting in clearly visible blue/green colonies.
(Other micro-organisms that possess b-glucosidase, such as enterococci, are inhibited by selective agents, lithium chloride, nalidixic acid and polymixin B).
In addition, phospholipase in listeria monocytogenes (and pathogenic listeria ivanovii) hydrolyses lecithin in the medium to produce a distinctive opaque white halo around the colony.
The selectivity of the medium is further enhanced by the addition of ceftazidime and amphotericin B, which inhibit other background flora, such as bacilli, yeasts and moulds.
Studies have shown the OCLA plate to have superior performance to Palcam and Oxford medium for the isolation of listeria monocytogenes.
