Gélose

The gélose is a nutritive substance supporting or inhibiting ( according to its composition) the proliferation and the development of the bacteria. It is thus about the Culture medium of the bactéries.
It is used in the laboratories to determine the level of effectiveness of new antibiotics, to test bacterial resistance with respect to already known products, or more simply, to insulate or cultivate bactéries.
The gélose is different from the bubble, most of the time of ox bubble, by its which had solidity, in its composition, with the presence of agar-agar to a total value of 20 g/L approximately.

Types of géloses

According to its contents, a gélose can support the growth of certain bacteria with depend on the others; it is what is called the selectivity . Moreover, some géloses are differential , i.e. the aspect of the bacterial colonies which are formed there can allow, up to a certain point, to deduce from which type of bacterium it acts. Here some géloses current in the laboratories of Microbiology.

  • Gélose with blood : it is a gélose bright red containing of the red Globules (often of the blood of sheep). Not very selective, it however makes it possible to appreciate the Hémolyse which certain bacteria carry out. The bacteria able to destroy the red globules completely (what is called a hémolyse beta) will form colonies surrounded by an easily visible clear zone on the red gélose; if the hémolyse is incomplete (hémolyse alpha), the zone of hémolyse will be less clear. A complete hémolyse is visible inter alia in the case of the Streptocoque of group A.

  • Gélose MacConkey : this gélose is used to test the capacity of the Bactéries to negative Gram has to ferment some Sucre S or sources of carbon; This medium contains biliary Sels and Violet of gentian which make it possible to eliminate the bacteria with positive Gram. It contains moreover one indicator of pH (red neutral) and sweetens it of which have wants to test the fermation (Lactose, Sorbitol, Arabinose, Maltose…). Degradation by fermentation of this sugar causes an acidification which makes transfer the coloring of the colonoes to the pink sharp thanks to the indicator of pH. The bacteria which do not ferment sugar tested remain with neutral pH and have a beige color. The gélose MacConkey is employed inter alia for the culture of the Entérobactéries and the Pseudomonas aeruginosa.
  • Gélose chocolate : it has nothing to do with the Chocolat. Its brown color comes from the cooked blood which uses its composition. The chocolate gélose is adapted to cultivate certain capricious bacteria in terms of growth factors. In addition to the cooked red globules which release from the nutritive substances, the chocolate gélose often contains some additives required by certain bacteria. One adds to it also antibiotics intended to prohibit the growth of certain organizations, in order to better select the colonies to be made push. This gélose is used inter alia cultivating Neisseria gonorrhoeae and Haemophilus.

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