Culture medium

See also: Medium

A culture medium is a support which allows the culture of cells, of Bactérie S, of Levure S, Moisissure S in order to allow their study. In theory, the cells find in this medium the essential components for their multiplication in great number, quickly, but also sometimes of the elements which will make it possible to privilege a bacterial kind or a family. Thus, according to the goal of the culture, it is possible to place the micro-organisms under optimal, or completely unfavourable conditions.

It is composed of a base (Agar-agar, water, mineral…) as well as indicator of pH or reaction of Oxydoreduction to allow to formulate assumptions on the kind.

There exist also culture mediums which have the same function, but these mediums do not contain a Agar-agar, they are thus completely liquid.

This article will detail the characteristics of the culture media referring to the Microbiologie.

Concept of minimum medium

A minimum medium is a Milieu comprising the chemical elements strictly necessary to the bacterial Croissance, in a form usable by bacteria not having a particular requirement.

  • Composition of a minimum medium :

    • a source of carbon and energy, generally the Glucose .
    • a source of potassium and phosphorus : K2HPO4
    • a source of nitrogenizes and of sulfur : (NH4) 2SO4
    • a source of magnesium : MgCl2
    • a source of calcium : CaCl2
    • a source of iron : one employs iron citrate (the citrate has as a role to maintain iron in solution)
    • a source of trace elements : salts of Cu, Zn, Co, Ni, B, Ti
    • a source of Water , essential to any form of life: one uses the distilled water ( sterile )
    • a plug pH : it makes it possible to maintain a pH correct even optimum: KH2PO4 for example

  • In the absence of one of these components , the bacteria do not develop, because they cannot synthesize these products.

  • It is the addition of factor (S) of growth suitable (S) which makes it possible demanding bacteria to develop.

Empirical culture medium

An empirical culture medium known as is a medium whose one does not know the composition exactly.

Thus, in the standard medium heart-brain , there is water, agar-agar, hydrolysat of heart and brain without one knowing the qualitative and quantitative aspects of them. It will thus be used only for the growth of the bacteria, it does not have a selective effect.

Selective culture medium

The selective culture media known as allow only the culture of certain kinds of Micro-organisme S. For that one adds elements which inhibit the growth of the undesirable micro-organisms like the Sodium chloride with strong concentration, the Thiosulfate of sodium, the purple Cristal… The added elements are selected according to the characteristics of the required micro-organism. These mediums are used for the analysis of a polybactérien taking away.

Examples of selective mediums:

  • medium S: it allows the growth only Salmonellas and of Shigelles
  • medium of Sabouraud: it allows the growth of the mushrooms
  • gélose Kanamycine - Vancomycine, known as " Kana-Vanco" or Kv: it prevents the growth of the bacteria with positive Gram (action of the vancomycine) and of the majority of the enterobacteries (action of Kanamycine). On this medium, push preferentially strict anaerobic bacteria.

Culture medium enriched

They contain, in addition to the basic components, of the components essential to the bacteria, that those cannot synthesize. They are mediums used for obtaining the bacteria known as demanding .

For example: mediums with fresh blood (the Sang is rich in various nutrients). Mediums with serum, egg yolk.

Ordinary medium

They allow the culture of the bacteria which do not have a particular nutritive requirement, (nondemanding bacteria ). The composition of these mediums is simple and without effect of selection.

An ordinary example of medium could be the nutritive gélose .

Synthetic medium

These are mediums whose one knows the chemical composition exactly, as well from a qualitative point of view as quantitative.

They are used in the search for a precise enzymatic reaction. They are the mediums most usually used.

For example: one will use the medium Tryptophane to reveal the presence of tryptophanase (a Enzyme) by the production of Indole. Tryptophan is there in sufficient quantities to allow an interpretable result; it would not have been in the same way if the medium had contained only beef hydrolysat.

Semi-synthetic medium

One knows their exact composition only for certain components (from a quantitative point of view, for the products having an interest, like the growth factors .)

Other components being present in an empirical way.

See too

Random links:Proconsul (primate) | Michel Guerry | Sylvain Nouet | Hermann Hoffman | Alexandre Pierre Freslon | Description_d'imprimeur_de_post-scriptum