Egg (gélose)

Interest

This medium makes it possible to explore the lipolytic activity of the Micro-organisme S:

In food Microbiology : the micro-organisms having a lipolytic activity can proliferate in rich foods in milk and derived, meats and be at the origin of Altération S of this food.
In systematic microbiology : the study of the lipidic Métabolisme intervenes in the differentiation of the species, inside the kinds Bacillus, Pseudomonas, Flavobacterium, Clostridium, Neisseriaceae.

Principle

The egg yolk contains:

Of the lecithins which are Phospholipide S which can be hydrolized by a lécithinase.
Of the triglycerides being able to be hydrolized by a lipase.
a lipoprotein being able to be hydrolized by a lipoprotéase.

It also contains other Lipide S, in the form of complex lipo-proteinic which returns the reading of the delicate lécithinase and which, opacifies the medium.

the lipoprotéinases release from soluble lecithins, the Protéine S and the lipids, which results in an explanation around the culture.
the lécithinase leads to the soluble formation of Choline and a lipid not very soluble which precipitates and led to an opaque zone around the culture.
lipase leads to the precipitation of Fatty-acids giving place to an opaque white edging, being able to be confused with lecithin, but the opaque zone is, less important here than that of the lécithinase.

Composition

A ordinary Gélose or tripticase soya, added with egg yolk diluted to the 1/2 in distilled Water sterile, until obtaining a final concentration of 10% (either 2mL in 20mL).

Results

One sows the gélose by making scratches thick power station. Two aspects are observed:

the opacification of the gélose around the scratch of sowing: lécithinase.
appearance of a transparent zone around the culture: lipo-protéinase.

to see too

Culture medium
Culture media (list)

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