What are some examples of selective media

Nutrient medium

Synonyms: culture medium, growth medium

1 definition

A Nutrient medium is a sterile matrix with defined environmental conditions. Culture media are mainly used in microbiology and are used to cultivate microorganisms or human or animal cells.

2 classification

2.1 ... according to consistency

A distinction is made between two types of culture media based on consistency:

The transition between solid and liquid nutrient media is fluid and depends, among other things, on the agar or gelatine content, which ensures the thickening of a nutrient medium. Culture media with a lower agar content are sometimes delimited as the third group of so-called "semi-solid" media.

2.2 ... according to nutrient content

Another dimension is the division of the nutrient media according to the nutrient composition. A distinction is made here:

  • Mineral medium
  • Minimal medium
  • Minimal medium with growth substances
  • simple complex medium
  • Complex medium

2.3 ... according to the objective

  • Selective nutrient media or selective media: nutrient media whose nutrient content or composition only allow the growth of certain microorganisms or cells.
  • Differential culture media or differential media: culture media that allow the growth of several microorganisms used, but are composed in such a way that distinguishable colonies form.

Some culture media can combine both of the above properties, e.g. MacConkey agar or mannitol salt agar.

3 application

Liquid Culture media are used:

Festivals Culture media are mainly used for analysis purposes because they also enable quantitative determination. Since the multiplying microorganisms cannot freely distribute themselves in the medium, a visible point or spot forms around each initial germ. The number of these CFU (colony-forming unit) allows a conclusion to be drawn about the original number of germs.

The process of introducing samples into or onto a nutrient medium is called inoculation.

4 composition

In addition to water, culture media mainly contain culture-specific nutrients and salts. The nutrients are also called substrates and in most cases are carbohydrates, proteins and fatty acids. Nutritional salts provide ions and molecules that are essential for the organism, such as ammonium, potassium, sodium, magnesium, phosphate and sulfate.

Other possible components are:

5 Manufacturing

To produce a nutrient medium, the nutrients and additives are mixed together according to a recipe and dissolved in demineralized water (possibly under flowing steam). This is followed by sterilization (usually in an autoclave). Additives that would be destroyed by the sterilization can then be added through a sterile filter.

Ready-to-use culture media are also often used in practice.