Bacterial lecithinases are of special interest because of the possible role of these enzymes in pathogenicity. Lecithinases or phospholipases are enzymes released by bacteria that have the ability to destroy animal tissues. Phospholipid complexes are usually emulsifying agents occurring in tissues, serum and egg yolk. Lecithin is a normal component of the egg yolk. Bacterial lecithinases break down this lecithin to an insoluble diglycerides resulting in an opaque halo, surrounding the colony when grown on the egg yolk agar medium.
In egg yolk agar, the lipoprotein component Lecithovitellin can also be split by lecithinase into phosphorylcholine and an insoluble diglyceride, which results in the formation of a precipitate in the medium. This precipitate occurs as a white halo, surrounding the colony that produces lecithinase enzyme. The opalescence created is due to the release of free fat. Lecithinase activity is used to characterize several gram positive and gram negative bacteria.