Chromogenic L-Mono Listeria Differential Agar is based on the formulation of Ottaviani and Agosti and is used for isolation and cultivation of Listeria monocytogenes used for selective identification and differentiation of Listeria monocytogenes. Listeria monocytogenes is a gram-positive foodborne human pathogen responsible for serious infections in pregnant women that may ultimately result in abortion, stillbirth, birth of a child with neonatal listeriosis and meningitis or primary bacteremia in adults and juveniles. The pathogenicity of Listeria ivanovii for humans is uncertain.
This medium is based on the specific chromogenic detection of ß-glucosidase activity, rhamnose fermentation and PIPLC activity. Listeria species hydrolyse the purified chromogenic substrate in the medium giving blue coloured colonies. Since ß-glucosidase activity is specific for Listeria species, other organisms cannot utilize the chromogenic substrate and therefore give white colonies. Differentiation between Listeria species is based on the property of rhamnose fermentation and PIPLC activity. The colonies of L.monocytogenes appear bluish green with a yellow halo (rhamnose positive) while the colonies of L.ivanovii appear bluish green without a yellow halo (Rhamnose negative).
The differentiation of L.mono and L.innocua is based on PIPLC phosphatidylinositol-specific phospholipase C activity. Phospholipase C enzyme hydrolyses the purified substrate (TS 031) added to the medium resulting in an opaque halo around Listeria monocytogenes colonies. L.ivanovii also demonstrates PIPLC activity however since it does not ferment rhamnose it can be easily distinguished from L.monocytogenes.