Culture media: Types, Nutritional requirement, Raw material, Factor affecting of bacterial growth

Culture media

Culture media is that nutrition medium in which bacteria is grow. Culture media contains all essential materials which is required for growth and development.

All different types of bacteria cannot be grown in a single culture medium so different types of culture mediums are used for growth of different bacteria. We need this for about bacteria for any medical helps.

Culture media is divided into three categories:

1. Based on consistency

Based on consistency, culture media is of three types: solid, semi solid and liquid. Agar is used as solidifying agent, if agar is used 1.52% then it is solid medium, if agar is used less than 0.5% then medium is semi-solid, if agar is absent then medium is liquid.

2. Based on composition

For the growth of bacteria, different composition is required like energy source, carbon source, nitrogen source, water, growth factors and salt. The synthetic medium is prepared by using pure ingredient whose composition is known, where as in non-synthetic medium, the composition is not known and impure. It is depended upon the quality or quantity of material which is used to prepare culture media.

3. Based on application

In which we create culture media according to need of bacteria or based of application of bacteria:

1. Basic culture medium:- This is the general culture medium which contains all essential element and for growth of all types of primary bacteria.

2. Enriched medium:- It is for those bacteria, which need extra nutritional material. Extra nutritional material like blood, serum and yolk.

3. Enrichment medium:- It is designed for some a specific type bacterium and in this media antibiotic is used for reduce on wanted bacteria and the concentration of desired bacteria is increase.

4. Selective medium:- These are specially design culture media made for special or anyone bacteria.

5. Differential culture media:- This medium is a liquid medium in this metabolic dye is used to identify the different colonies by different colour.

6. Transport culture media:- This nutrition medium is used when the specimen is not used very soon. This media is prevented from drying. It is used because, in cultural media bacteria is dead in around 7 days but if we need this after 15 to 20 days or after many days so we prepare in transport culture media.

7. Anaerobic culture media:- This medium requires for those bacteria which is grow in anaerobic medium. Hemin and vitamin K is the main sources of energy in this medium. This medium also contents 0.1% glucose, 0.1% thioglycolate, 0.1% aerobic acid.

8. Assay medium:- This culture media is used for study purpose, in which we have to know about the concentration of material which is used to make culture media. It is rigid perfect or not.

Nutritional requirement for bacterial culture medium

For the preparations of culture medium for bacteria following requirements are necessary:
1. Major macro nutrients
2. Major micro nutrients
3. Carbon energy sources
4. Growth factor
5. Vitamin

1. Major macro nutrients:- These elements are required in large amount.

A. Carbon:- Carbon is the main sources of organic compound and CO2. Iit is the main component of cellular material.
B. Hydrogen:- The main source of organic compound, it is the main component of cell water.
C. Oxygen:- It is the main constituent of cell material and cell water.
D. Sulphur:- It is the main constituent of some amino acids like cysteine, methionine and several coenzymes.
E. Potassium:- It is the main component of cellular inorganic cation and cofactor for certain enzymes.
F. Phosphorus:- It is the main component of nucleic acid, nucleotides and phospholipids.
G. Nitrogen:- It is the main component of nucleic acid, nucleotides and coenzymes.
H. Calcium:- It is the main component of inorganic cellular cation, co-factor for certain enzymes and a component of endospores.

2.  Major micro nutrients:- potassium, calcium, magnesium, iron, copper, cobalt, manganese and zinc required in little amount for enzyme functions and it can be provided in tap water or as contaminants of other medium ingredients.

3.  Carbon energy source:- carbon is the main source of energy in the form of co2 sources. The photosynthetic bacteria are required CO2 and sunlight, chemosynthetic bacteria required CO2 and chemicals as a source of energy like ammonia, nitrate etc.

4.  Growth factor:- all the bacteria require a small amount of organic compound for growth because they are essential as growth factor. Purine and pyrimidine, this is essential for DNA synthesis.

5.  Vitamin:- vitamins act as co enzymes for the growth of purine pyrimidine, the growth factor is identical with vitamins of B group- thiamine, riboflavin, nicotinic acid, pyridoxin and vitamin B12.

Raw material used for culture media

That material, which are used in making of culture media.

1. Water:- In bacteria 70-80% of water is present and it is used as a vehicle for flow of nutrients. So, water is necessary for preparation of culture media but distilled water is preferred to use because tap water contain magnesium, which may be react with phosphate present in peptones and may be inhibit the growth of bacteria.

2. Peptone:- It is hygroscopic in nature (which attract water from its surrounding). It is complex mixture of partially digestive protein obtain from meat, heart muscle, fibrin, soya meat etc. It contains certain growth factor, important constituent like, protease, amino acids, magnesium and potassium, which supply nitrogenous material and also act as a buffer.

3. Meat extract:- It contain gelatine, protease, purines and growth factor, which is essential for bacteria and it prepared from fresh lean meat by hot water extraction process.

4. Agar:- It is important material for culture media and it is used for preparation of solid media. It is long chain polysaccharides obtained from seaweeds algae. It acts as a good solidifying agent. It has no nutritional value in media and it is easily available.

5. Yeast extract:- It consist of the cell contents of yeast without the cell wall, it contains carbohydrates, amino acids, growth factor and  inorganic salts. Used mainly as a source of vitamin and substitute for meat extracts.

Factor affecting of bacterial growth

There are many physical conditions, which are essential for bacterial growth or it affect the growth of bacteria.

1. Nutritional concentration:- Bacteria requires different nutritional supplement like purine, pyramided, vitamin and macro nutrients in a certain limit. When the concentration of nutritional supplement is increases then the growth of bacteria is also increases but after a certain limit the growth of bacteria is remain constant.

2. Temperature:- The bacteria show maximum growth in the temperature rays 45°C to 70°C maximum growth. The lowest temperature (30°C) where bacteria allow the grow is called minimum temperature and the highest temperature after that (75°C) bacteria is started to kill is called maximum temperature.

If in the graph of line grows a straight in the increasing manner up to optimum temperature, then after the growth is decreases. Some bacteria are growth in very high temperature is called hyperthermophile bacteria, and some bacteria in very low temperature, they are called  psychrophiles bacteria.

3. pH:- All bacteria grow in certain pH range. Acidophil bacteria show maximum growth in the range of 3 to 5, basophil shows at 8 to 10 and neutrophile bacteria in 6 to 8.

4. Ions and salt:- All bacteria require a small amount of ions K+, Ca2+, mg2+ Fe2+ etc for synthesis of protein and enzymes and bacteria can also tolerate some amounts of salt. These ions and salts help in osmosis but at high concentration due to reverse osmosis bacteria’s kills. Some bacteria require high concentration of salt, called halophiles bacteria.

5. Osmotic pressure:- Bacteria can tolerate osmotic variation due to mechanical strength of cell wall. They can grow media with varying contents of salts, sugar and other solutes.

6. Water:- Water is very essential factor for growth of bacteria. The water in culture media decided the metabolism and physiological activity of bacteria. All nutrients sugar and salt are dissolved in water which is made available for bacteria.

7. Gaseous requirement:- For the growth of bacteria Oxygen and CO2 gas is required. Oxygen is required for aerobic bacteria and CO2 is required for photosynthesis and chemosynthetic bacteria.