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| Listeria monocytogenes on Palcam agar. The colonies are green and surrounded by a black zone. |
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Listeria innocua on Palcam agar.
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A selective and differential diagnostic medium for Listeria. It is highly selective due to inclusion of lithium chloride, ceftazidium, polymixin B and acriflavine hydrochloride. A double indicator system is used as the medium contains aesculin and ferrous ions as well as mannitol and phenol red. Listeria hydrolyses aesculin, producing colonies surrounded by a black zone. Enterococci and staphylococci ferment mannitol, producing colonies surrounded by a yellow zone, due to lowering of the pH in the medium. Listeria is mannitol negative.
The picture below is of an uninoculated medium.
Click on the picture to see an enlarged version. |
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