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Types of Microbiological Medium

Due to the different nutrition needed, there are many types of medium. It is estimated that there are thousands of different medium at present, which can be divided into several types according to the content, physical state, and different purposes of use. Let us learn about microbiological medium and its types.


1. Medium types according to the composition

The medium can be divided into three types: synthetic medium, natural medium and semi-synthetic medium according to its components.


(1) Synthetic medium

The various components of the synthetic medium are all known chemical substances. The chemical composition of this medium is clear, the composition is accurate, and the reproducibility is strong, but the price is more expensive, and the growth of microorganisms in this medium is slow.


(2) Natural culture medium

Made from natural substances, such as steamed potatoes and regular beef broth. The former is used to cultivate molds and the latter is used to cultivate bacteria. The chemical composition of this type of medium is not constant and difficult to determine, but it is easy to prepare and rich in nutrients, so it is often used.


(3) Semi-synthetic medium

On the basis of natural organic matter, appropriately add inorganic salts of known ingredients, or add some natural ingredients on the basis of synthetic medium, such as types of agar used in microbiology: potato and glucose to cultivate molds. This type of medium can more effectively meet the needs of microorganisms for nutrients.


2. Medium types according to the physical states

Medium can be divided into three types: solid medium, liquid medium and semi-solid medium according to its physical state.


(1) Solid medium

 A coagulant is added to the culture medium, such as agar, gelatin, silica gel. Solid medium is often used for microbial isolation, identification, counting, and preservation of bacterial species.


(2) Liquid medium

No coagulant is added to the liquid medium. The composition of this medium is well-proportioned, and the microorganisms can fully contact and utilize the nutrients in the medium, which is suitable for physiological research. Due to the high fermentation rate and convenient operation, it is also often used in the fermentation industry.


(3) Semi-solid medium

It is a semi-solid state by adding a small amount of coagulant to the liquid medium. It can be used to observe the movement of bacteria, identify bacterial species and determine the potency of bacteriophages.


3. Medium types according to the microorganism types

According to the types of microorganisms, the medium types in microbiology can be divided into four categories: bacterial media, actinomycete media, yeast media, and mold media.


4. Medium types according to its use

According to special uses, the medium can be divided into enriched medium, selective medium and differential medium.

(1) Enriched medium

It is to add the extract of blood, serum, animal and plant tissue into the medium to cultivate some microorganisms with strict requirements.

(2) Selective medium

It is a medium designed according to the special nutritional requirements of a certain kind of microorganism or to some physical and chemical resistance. By using this medium, the required microorganisms can be separated from the mixed microorganisms.

(3) Differential medium

It is to add some reagents or chemicals into the medium to make certain changes after cultivating, so as to distinguish different types of microorganisms.

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