Different bacteria have different nutritional requirements, but the nutrients needed by bacteria should contain ammonia sources, carbon sources, inorganic salts and growth factors.

Protein：one of the most commonly used components, providing nitrogen source needed for bacterial growth and reproduction, containing peptones, peptides and a variety of amino acids, for the majority of bacterial growth used. Easily soluble in water and acid does not precipitate, not due to high temperature and solidification, for the amphoteric electrolytes have a buffering effect.

Meat dip：with fresh beef soaked, boiled and made of gravy. It contains soluble nitrogenous leachate and non-ammoniacal leachate, as well as some growth factors. It can provide ammonia and carbon source for bacteria, but the nitrogen content is too little to meet the needs of bacteria, so in the preparation of culture medium should be added 1% ~ 2% of peptone and 0.5% sodium chloride.

3、Beef paste： It is made from meat extract by heating and concentrating for a long time. Sugars are destroyed during heating, and its nutritional value is lower than that of meat extract, which can be used as the basic component of culture medium for identification of enterobacteria.

4、Sugars and alcohols：provide carbon source and energy for bacterial growth. There are many kinds of sugars and alcohols used in the preparation of culture medium, commonly used sugars are monosaccharide, disaccharide and polysaccharide; commonly used alcohols are mannitol, weimanol, etc. Glucose and sucrose are mainly used as carbon source and energy source. Glucose and sucrose are mainly used as the basic components of carbon and energy, while other sugars and alcohols are mainly used to identify the fermentation reaction done by bacteria.

5、Blood：blood contains a variety of nutrients, and can provide coenzymes, haemoglobin and other special growth factors, for the cultivation of bacteria with high nutritional requirements. It can also be identified according to the haemolysis phenomenon of bacteria in blood culture medium.

6、 Inorganic salts：provide a variety of elements for bacterial growth, such as potassium, sodium, iron, magnesium, calcium, phosphorus, sulfur and so on. The most commonly used are sodium chloride and phosphate, the former to maintain enzyme activity, regulate the osmotic pressure inside and outside the bacterium, the latter is a good source of phosphorus bacteria, and has a buffering effect.

7、Eggs and animal serum：not the basic ingredients, is necessary for the growth of certain bacteria nutrients, only for the preparation of special media. Such as the culture of Mycobacterium tuberculosis egg culture medium and culture of diphtheria bacillus lu's serum culture medium.

8、Growth factors：essential for bacterial growth, the need is small. Often in the liver extract, meat extract, alcohol mother extract and blood-containing medium to add vitamins, amino acids, purines, pyrimidines and other growth factors.

When preparing solid media, a coagulant is added to the liquid. Commonly used coagulants are agar, and in some cases, gelatin, ovalbumin, serum and so on. Agar is a kind of galactose gum extracted from stonewort, which can be dissolved in water when the temperature is above 98℃, and can be solidified into a gel state below 45℃, which is not decomposed and utilised by bacteria and has no nutritive effect.

Inhibitors and indicators are often added in the preparation of culture medium, which are not necessary for the growth and reproduction of bacteria, but are needed for selection, identification and judgement of results.

1、Inhibitors：selective inhibition, in the preparation of culture medium by adding a certain type of inhibitors, can inhibit the growth of non-detectable bacteria (non-pathogenic bacteria), and facilitate the growth of detectable bacteria (pathogenic bacteria), commonly used bile salts, Brilliant Green, sodium sulphite, sodium selenite, and some dyes and antibiotics and so on.

2、Indicator：add certain kinds of indicator in the culture medium to observe whether the bacteria use and decompose the sugar and alcohol in the medium. Commonly used are pink, methyl red, neutral red, bromocresol purple, bromo muscovado phenol blue and China blue and other acid-base indicator. Methylene blue is commonly used as a redox indicator.

1、Basic medium：It contains basic nutrients required for basic growth of bacteria, the most commonly used is meat infusion, commonly known as broth, mainly containing raw meat infusion and peptone, used for bacterial enrichment, testing, and is also the basic component for the preparation of other culture media.

2、Nutritional medium：blood, glucose, growth factors and other special ingredients are added to the basic medium for the growth of bacteria with high nutritional requirements and bacteria requiring special growth factors, the most commonly used ones are blood agar plate and chocolate blood plate.

3、Identification medium：add some specific substances, such as sugar, glycosides, alcohols, amino acids, proteins, etc. and indicators in certain medium to determine the biochemical reaction of bacteria, in order to identify and identify the medium used for bacteria. For example, sugar fermentation tubes, Kirschner's Iron Agar (KIA), iron-methylene blue agar and power-indole-urea (MIU) medium.

4、Selective medium： add inhibitors in the medium to inhibit the growth of stray bacteria in the specimen, which helps the growth of the selected bacterial species. Such as the culture of intestinal pathogenic bacteria Salmon - Shiga agar.

5、Special medium：some bacteria need special conditions to grow and reproduce, including anaerobic medium and bacterial L-type medium. The former is a medium for the cultivation of specialised anaerobic bacteria, and the latter is for the L-type of bacteria with cell wall defects.

1、Blood plate：suitable for the growth of all kinds of bacteria, general separation of bacterial test specimens should be inoculated with this plate.

2、Chocolate blood plate：containing V and X factors, suitable for inoculation of specimens suspected to have Haemophilus, Neisseria and so on.

3、Chinese blue plate or iron-methylene blue plate： inhibit gram-positive bacteria, promote the growth of gram-negative bacteria, is a better weak selective medium. Fermented Gram-negative bacilli have different colony colours on this plate, which is convenient for identification of bacterial species.

4、McConkey plate：medium strength selective, slightly strong inhibitory force, a few Gram-negative bacteria do not grow. Whether the bacteria can grow on the McConkey plate is a basis for the identification of non-fermenting bacteria.

5、Salmonella-Shiga agar：strong inhibitory force, used for the separation of Shigella and Salmonella. Because the selectivity is too strong, affecting the detection rate, it is best to use a weak selection plate to pair complementary.

6、Alkaline agar or TCBS agar：used to separate Vibrio cholerae and other vibrios from faeces.

7、Blood enrichment medium： used to separate common pathogenic bacteria from blood and bone marrow.

8、Nutrient broth：used for the enrichment of specimens and all kinds of bacteria.