This proprietary selective medium, which contains the substrate, lecithin, differentiates L. monocytogenes and L. ivanovii from other Listeria species. Oxoid Ltd, Basingstoke, England, provides it as a dehydrated basal medium and a lecithin supplement with a selective antibiotic supplement. Differential activity for all Listeria species is due to the addition of a chromogenic substrate. Follow the manufacturer's instructions. http://www.oxoid.com