How to make a culture medium? Make a culture
In preparationmediumIn the process, first use some glassware, such as test tubes, triangular bottles, petri dishes, beakers and straws. These utensils must be treated and washed according to different conditions before use. Some also need to be packaged and sterilized before they can be used.
1. Newly purchased glassware
After removing the dirt contaminated with the packaging, first wash it with hot soapy water, rinse it with running water, and then soak it in 1 to 2% industrial hydrochloric acid for several hours to remove the free alkaline substances, and then rinse it with running water. For large-capacity utensils, such as large flasks, measuring cylinders, etc., after washing, inject a little concentrated hydrochloric acid, turn the container so that its internal surface is stained with hydrochloric acid, pour out the hydrochloric acid after a few minutes, rinse it with running water, turn it upside down on the washing rack and dry the water before use.
2. Used glassware
All utensils that are indeed free of pathogenic bacteria or not contaminated by bacteria can be rinsed at any time after use. Straws that have absorbed chemical reagents can be soaked in water first, and then cleaned in a concentrated manner after a certain amount. Utensils that may be contaminated by pathogenic bacteria must be properly disinfected, the dirt must be removed, washed with soap, and then rinsed with running water. If utensils that cannot be washed with soap can be soaked in washing liquid for an appropriate period of time and then washed with water. The main ingredients of the washing liquid are potassium dichromate and concentrated stream acid, which are used to oxidize organic matter into soluble substances for rinsing. The washing liquid has a strong corrosive effect, and special care should be taken when using it to avoid splashing on clothes, body and other items.
Type of medium
Any nutrient matrix that is suitable for microbial growth and reproduction or accumulation of metabolites formulated in the laboratory is called a medium. Due to the different nutritional requirements of various microorganisms, different culture purposes and testing needs, there are many types of media. We can divide a wide variety of media into several types according to certain criteria.
1. According to whether the chemical composition of the medium is fully understood, the medium can be divided into natural medium, synthetic medium and semi-synthetic medium.
A. Natural culture medium refers to the use of various animal, plant or microbial raw materials, the composition of which is difficult to know exactly. The main raw materials used for this medium are: beef paste, wort, peptone, yeast paste, corn flour, bran, various cake powders, potatoes, milk, serum, etc. Although the chemical composition of the medium prepared with these substances cannot be known exactly, in general, the nutrients are relatively rich, the microorganisms grow vigorously, and the sources are wide, and the preparation is convenient, so it is more commonly used, especially suitable for the preparation of commonly used media in laboratories. The stability of this medium is often affected by factors such as the production plant or batch number. Buy the medium and go to the National Standard Products Network.
B. Synthetic medium Synthetic medium is a type of medium with fully known chemical composition and quantity. It is formulated with chemicals with known chemical composition. This type of medium has precise and reproducible chemical composition, but it is expensive, and microorganisms grow slowly, so it is only suitable for doing some scientific research, such as nutrition and metabolism research.
C. Semi-synthetic medium In synthetic medium, add one or more natural ingredients; or in natural medium, add one or more chemicals of known ingredients to form semi-synthetic medium. For example, potato sucrose medium, etc. This medium is most used in production practice and laboratories.
2. According to the physical state of the medium, it can be divided into solid medium, liquid medium and semi-solid medium.
The liquid medium is prepared in a liquid state, with the ingredients basically soluble in water and no obvious solids. The nutrients in the liquid medium are evenly distributed, making it easy to control the growth and metabolism of microorganisms.
B. Solid medium Add an appropriate amount of coagulant to the liquid medium to form a solid medium. Commonly used as coagulants are agar, gelatin, silica gel, etc. Agar is the most commonly used. Solid medium is widely used in practice. In the laboratory, it is used for the isolation, identification, detection of bacteria, counting, preservation, bioassay, etc.
C. Semi-solid medium If a small amount of coagulant is added to the liquid medium, a semi-solid medium is prepared. Take agar as an example, it is used in amounts between 0.2 and 1%. This medium can sometimes be used to observe the motility of microorganisms and sometimes to preserve strains.
3. According to the purpose of the medium, it can be divided into selection medium, proliferation medium,differential mediumWait.
A. Selection medium A medium in which a substance is added to the medium to kill or inhibit the growth of unwanted strains, called selection medium. Such as streptomycin, chloramphenicol, etc. inhibit the growth of prokaryotic microorganisms; while nystatin, griseofulvin, etc. can inhibit the growth of eukaryotic microorganisms; crystal violet can inhibit the growth of Gram-positive bacteria, etc.
In nature, different kinds of microorganisms often live together. In order to isolate the microorganisms we need, some nutrients that microorganisms particularly like are added to the ordinary medium to increase the reproduction rate of this microorganism and gradually eliminate other microorganisms. This medium is called proliferation medium. This medium is often used in species screening and selective growth. To some extent, proliferation medium is also a selective medium.
C. Identification medium Add certain reagents or chemicals to the medium to make indistinguishable microorganisms show obvious differences after culture, thus helping to develop a rapid identification of a certain microorganism. Such a medium is called an identification medium. For example, eosin blue medium used to check whether drinking water and dairy products contain intestinal pathogens is a commonly used identification medium.
Some media have the dual function of selection and identification. For example, Macquay medium, which is commonly used in food inspection, is an example. It contains bile salts, lactose, and neutral red. Bile salts have the effect of inhibiting bacteria other than intestinal bacteria (selective), and lactose and neutral red (indicators) can help distinguish lactose-fermenting intestinal bacteria (such asEscherichia coli) and intestinal pathogens that cannot ferment lactose (such as Salmonella and Shigella).
In addition, according to whether the nutrient composition of the medium is "complete", it can be divided into basic medium, complete medium and supplementary medium. Such terms are mainly used in microbial genetics. According to the purpose of the medium used for production, it can be divided into seed medium and fermentation medium. There are also living tissue media specially used to cultivate parasitic microorganisms such as viruses, such as chicken embryos, etc.; inorganic salt medium specially used to cultivate autotrophic microorganisms, etc.
