What is culture medium? What are the applications of liquid and solid media for bacterial testing?

Culture media refers to artificially formulated mixed nutrients that are suitable for the growth and reproduction of microorganisms or the production of metabolites.

SolidCulture mediumThe differences with liquid media are:

1. The composition is different

Liquid medium is liquid at room temperature, like water.

Solid medium is to add coagulant (generally agar to the liquid medium), which is solid at room temperature, like cold powder.

2. Different roles:

The liquid medium has fast mass transfer, fast nutrient supplementation, and fast diffusion of metabolites. Liquid media are generally used in industry.

Solid media are generally used for isolation, culture preservation, and research.

3. Different meanings:

Liquid medium: The equivalent of solid medium, which is a microbial or animal and plant cell.

of liquid medium. It has the advantages of aeration culture and shaking culture. Under quiescent conditions, a nutrient barrier is formed around the cell or cultured cells, and nutrient intake is hindered.

Solid medium: The medium that is solid at the general incubation temperature is called solid medium. Add the left and right agar to the liquid medium, heat it to 100 degrees to dissolve, cool it at 40 degrees Celsius and solidify, so that it becomes a solid state, that is, a solid medium.

Both solids and liquids are available and can be determined depending on the specific range of applications. Solid medium has two functions: enrichment and separation, and liquid medium mainly plays an enrichment role. The identification medium is generally solid, such as eosin blue solid medium, and the liquid medium can be used to identify purebred microorganisms, such as sugar fermentation medium is the identification medium.

Theoretically, liquid media can transfer mass, replenish nutrients quickly, and diffuse metabolites quickly. From the perspective of practical application, it is very telling that the expansion of culture and industrial application are all cultivated with liquid. Solid culture media are generally used for isolation, culture preservation and research.

Classification of microorganisms:

Selective medium: a type of medium designed according to the special nutritional requirements of a microorganism or its resistance to a certain chemical and physical factors, which has the function of turning the inferior bacteria in the mixed bacterial sample into the dominant bacteria, and is widely used in the field of strain screening.

Identification medium: A type of indicator that can react with the colorless metabolites of the target bacteria is added to the composition, so as to achieve the medium that can easily find out the colony of the target bacteria from the similar colonies only by distinguishing the color with the naked eye. For example, eosin blue lactose medium (EMB).

Liquid medium.

It is mainly used for the expansion of microbial culture.

The medium is in accordance with the physical properties.

It can be divided into liquid culture medium, semi-solid medium and solid medium. Liquid medium is often used for the expansion of microbial culture, semi-solid medium is often used to observe the movement of microorganisms and preservation of strains, and solid medium is often used for the parting and identification of microorganisms.

The liquid medium has the advantage of being able to be prepared for aeration and shaking culture, which can increase the oxygen supply of microorganisms and allow microorganisms to fully contact nutrients under the condition of ventilation or shaking. Therefore, the liquid medium favors the cell growth of microorganisms, thereby increasing the number of microorganisms.

Solid media, on the other hand, usually contain agar that hinders the movement of microorganisms. Under quiescent conditions, agar will form a nutrient barrier around the anterior finger of the microbial cell during the culture process, which will affect the nutrient absorption of microorganisms and lead to slow microbial growth.

You can choose the medium and distinguish between liquid and solid media.

It can be determined according to the specific application area. Solid medium is widely used for the isolation, identification, preservation, counting and observation of colony characteristics of microorganisms. The medium in a liquid state is called a liquid medium or culture broth, fermentation broth.

Liquids are one of the three major forms of matter. It does not have a definite shape and is often influenced by the container. However, its volume is fixed under constant pressure and temperature.

The distance between the molecules of the liquid is farther, the molecular motion is more intense, and the attraction between the molecules is less. Increasing or depressurizing generally vaporizes the liquid into a gas.

The medium is sterilized by autoclave or filtration before use. To prevent pollution, attention should be paid to the following:

Bacterial, fungal and mycoplasma sterility tests can be used to confirm and rule out the working cell bank, the working seed batch of the virus, and the medium used and its added components to be contaminated.

At the same time, the sensitivity of the sterility test medium should be verified. In actual production, a small amount of nutrient agar can be added from the prepared culture medium and cultured in a constant temperature incubator, and whether there is pollution can be observed for 48 hours.

Others: autoclave equipment and filtration and sterilization equipment should be verified to ensure sterilization and sterilization effect; The former should be validated before production and every 6 months thereafter, and the latter should be validated before and after each sterilization.

In addition, the toxic area should be strictly separated from the non-toxic area, and there should be an independent air purification system and incubator, and the toxic area should maintain a relatively negative pressure on the non-toxic area to prevent the contamination of cultured cells by the virus.

There are three types of culture media according to their physical state: solid, semi-solid, and liquid.

Solid media can be made into plate, bevel, and high-rise media as required. Plate medium is often used for bacterial isolation, colony characterization observation, antimicrobial susceptibility test, and viable bacteria counting. Inclined medium is often used for culture preservation; The high-level medium is mostly used for silent biochemical experiments of bacteria.

Semi-solid medium is mostly used for bacterial motility observation, that is, the kinetic test of bacteria, and is also used for the preservation of strains.

Liquid media are commonly used for the expansion of bacteria in production and experiments.

Semi-solid medium should be used for the growth of bacteria, I think.

As for the strains, you can use more than one strain to see what the difference is.