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Microbiology Test

Main Ingredients of Chromogenic Culture Media

Chromogenic culture media is generally used in isolation medium by adding specific enzyme substrates for detecting certain bacterial species. The substrate is composed of a chromogenic group and microbial metabolites, usually colorless. However, under the action of specific enzymes, the chromogenic group is freed and displays a certain color. The identification of bacterial species can be made by directly observing the color of the colony. Chromogenic Culture Media is like soil, which is the base for the survival and development of excised materials in tissue culture. Therefore, in every aspect of tissue culture medium, it is important to grasp the medium, understand its composition and preparation methods.

Currently, most media are composed of five types of substances including inorganic nutrients, carbon sources, vitamins, growth regulators, and organic additives.

Inorganic nutrients in the chromogenic culture media

Inorganic nutrients are mainly composed of large and trace elements. For the large elements, nitrate nitrogen or ammonium nitrogen is usually used as the nitrogen source in the medium, but nitrate nitrogen is used more often in the medium, and a mixture of nitrate nitrogen and ammonium nitrogen is also used. Phosphates and sulfates are commonly used to provide phosphorus and sulfur. Potassium is the main cation in the medium, and its quantity tends to increase in modern media. The requirements for calcium, sodium, and magnesium are relatively low. Sodium and chloride needed in the medium are provided by calcium salt, phosphate, or trace nutrients.

Trace elements include iodine, manganese, zinc, molybdenum, copper, cobalt, and iron. Iron ions in the medium mostly form a chelation with iron, that is, a mixture of FeSO4 and Na2-EDTA (chelating agent).

Carbon source in the chromogenic culture media

The photosynthesis of cultured plant tissues or cells is weak. Therefore, some carbohydrates need to be added to the medium for them. The carbohydrate in the medium is usually sucrose. In addition to being the carbon source and energy source in the medium, sucrose also plays an important role in maintaining the osmotic pressure of the medium.

Vitamins in the chromogenic culture media

Addition of vitamins in the medium is often beneficial to the development of explants. The vitamins in the Chromogenic Culture Media belong to the vitamin B family, and the effective vitamins include vitamin B1, vitamin B6, biotin, calcium pantothenate, and inositol.

Organic additives in the chromogenic culture media

Includes artificially synthesized or natural organic additives. The most commonly used are casein hydrolysate, yeast extract, coconut milk, and various amino acids. In addition, agar is also the most commonly used organic additive, which mainly serves as a support for the medium, making the medium solid for the cultivation of various explants.

Growth regulators in the chromogenic culture media

The commonly used growth regulators roughly include the following three categories:

  • Plant hormones, such as indoleacetic acid (IAA), naphthaleneacetic acid (NAA), and 2,4-dichlorophenoxyacetic acid (2,4-D).

  • Cytokinins, such as zeatin, 6-benzylaminopurine (6-BA or BAP), and kinetin (Kt).

  • Gibberellins. The only type of gibberellin used in tissue culture is gibberellin acid (GA3).

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