Listeria monocytogenes is a pathogenic bacterium which can cause serious food poisoning. Since L. monocytogenes and L. innocua have similar biochemical properties, they cannot be differentiated on traditional media (PALCAM, Oxford).
On EZ-CHROM Listeria, L. monocytogenes colonies have a specific blue color surrounded by a white opaque halo. The Colorex Listeria method allows detection of negative samples in only 2 days. This method requires only a single half Fraser broth enrichment step.
Confirmation of positive samples can be performed by picking a suspect colony directly from the Colorex™ Listeria plate and transferring it to Colorex™ Identification Listeria giving a next day confirmation that the isolate is indeed L. monocytogenes.
EZ-CHROM Listeria is 100% sensitive for L. monocytogenes which typically appear as blue colored colonies with convex colony shape, 1.0-2.5mm in diameter with a halo. Blue colonies may appear after 24 hours. Two species of Listeria display blue colonies with halos on EZ-CHROM Listeria Agar, L. monocytogenes and L. ivanovii. To differentiate these species you are required to set-up a confirmation plate or run a rapid biochemical identification test strip such as Microgen™ Listeria ID.
Other Listeria species such as Listeria innocua appear as Blue colonies with no halo on EZ-CHROM Listeria Agar
*EZ-CHROM plates are a Colorex™ product, EZ-CHROM powder is a CHROMagar™ product