Casein is the predominant phosphoprotein that accounts for nearly 80% of proteins in milk. Some bacteria has the enzymatic
capability to degrade casein. Casease is the exoenzyme involved in this process. Simplest medium used for casein hydrolysis
testing is Milk agar.
Add 1-2 ml of sterile skimmed milk to every 10 ml nutritive agar medium (melted).
Homogenize then pour the mix in Petri dishes. Control sterility.
Harvest a well isolated colony and disperse it on the Milk agar surface. Incubate at
37 °C, 24 hours. If strain can produce casease, then a clear zone can be seen
around the colonies.
1. H. Raducanescu, V.Bica-Popii,1986. Bacteriologie veterinara, Ed. Ceres,
|Casein positive colonies on Milk agar
(clear areas around colonies)
(c) Costin Stoica