Culture media and types

Giving basic concepts regarding culture media and its classification on the basis of different properties like physical state, chemical composition and utility purposes.

1. Culture media and types Anup Muni B ajracharya

2. Culture medium food that is use in the laboratory for the growth of bacteria, molds and other micro-organism. nutrient preparation in which micro-organism are grown in the laboratory, the growth itself is called a culture. Robert Koch- discovered and developed the use of culture medium. the first medium in bacteriology- potato agar

3. C omposition of media i ) Agar ii ) Peptone iii ) Extracts( Meat extract, yeast extract ) iv ) Carbohydrates v ) Water

4. Agar Agar is solidifying agent an impure polysaccharides obtained from certain red marine algae. liquifies at about 100 c solidified at 45 c.

5. Peptone water soluble product obtained from the breakdown or hydrolysis of animal or plant material such as meat scraps, muscles, gelatin, milk protein etc. Hydrolysis is brought by the action of acid and enzymes such as trypsin and pepsin

6. Extracts Eukaryotic tissues (yeast, beef muscles, liver,brain ) are extraced by boiling and then concentrated to a paste or dry to powder. Those which are extracted from yeast cells are called yeast extracts. Meat extract Yeast extract

7. Carbohydrates The bacteriologist use carbohydrates to enrich media for growth, pigmentation and to determine whether the organism can produce acid or gas by using it . M ost commonly use carbohydrates are glucose, sucrose, lactose, maltose etc.

8. Water essential for growth of all micro-organism. used in microbiology lab for dissolving media

9. Classification of culture media On the basis of physical state of the media, it can be classified as a ) Solid media b ) Liquid media c ) Semi- solid media a) Solid media:- media which are solid in state. Agar is the major solidifying agent ,added in concentration of 1.5% for plates, slant media. Eg : Nutrient agar, Macconkey agar . b) Liquid media (broth):- media which are in liquid state. This form of media don't contain agar or any solidifying agent . Eg :- Nutrient broth, Macconkey broth . c) Semi- solid media:- This form of medium is prepared by adding a small amount of agar (0.2-0.5%)to a fluid medium. The consistency of this media is jelly like, the consistency between solid and liquid. Eg :- Hugh Leifson's media, SIM media.

10. Chemical composition On the basis of chemical composition, media are of two types. chemically-defined (synthetic) medium b ) complex (undefined) medium A chemically-defined (synthetic) medium: It is one in which the exact chemical composition is known. It is generally made from various chemicals that are highly purified and precisely defined. A complex (undefined) medium is one in which the exact chemical constitution of the medium is not known. complex media usually contain complex materials of biological origin such as blood or milk or yeast extract or beef extract, the exact chemical composition of which is obviously undetermined.

11. Utility On the basis of utility purpose media are of following types a ) Basal Media( General Purpose Media):- simple media which support the growth of microorganism that do not have special nutritional requirements. designed to grow as many as possible of the organism commonly used in general bacteriological laboratory. E.g . Nutrient agar, Nutrient broth.

12. Enriched Media used for the cultivation of certain microorganism that have elaborated requirements for specific nutrients. For the growth of fastidious micro-organism such as Haemophilus influenza, Streptoccocus , Neisseria etc. In such media, some addition as supplementary foods are supplied besides the common nutrients. Such as blood, egg, serum, vitamins ,peptones, aminoacids to a basal media. e.g. Blood agar, chocolate agar, egg yolk medium.

13. BLOOD AGAR Enriched Media

14. Chocolate agar

15. Selective Media A selective media is one which has a components added to it which will inhibit or prevent the growth of certain types or species of bacteria and/or promote the growth of desired species. Such media contains some selective substances that supports the growth of desired organism while inhibiting the growth of unwanted organism in a mixture . E.g . Macconkey Agar is selective media for Gm - ve bacteria because it contains selective agents like bile salts and crystal violet which inhibit the Gm + ve bacteria. XLD agar selects for Salmonella Shigella species.

16. Differential Media Differential media consists of indicator , dyes or other substances to differentiate microorganism. These types of media are also known as indicator media and these media incorporate some substances i.e. changed visibly as a result of the metabolic activities of particular organism. Eg : Macconkey Agar contains the indicator neutral red which differentiate lactose fermenting from Non- Lactose fermenting organism.

17. Macconkey Agar-Differential media

18. Blood agar- Differential M edia

19. Enrichment media:- These are fluid media that increases the number of pathogens by containing enrichment and a substances that discourage the multiplication of unwanted bacteria . For e.g :- Alkaline Peptone Water is used as enrichment media for vibrio species. The pH of the media is high (8.5-9.2) that supports the growth of vibrio species and is inhibitory to other organisms.

20. Transport Media These are media that are devised to maintain the viability of a pathogen and to avoid over growth of other contaminants during transit from the patient to the laboratory. Their use is particularly important when transporting microbiological specimens from health centre to the district microbiology lab. E.g :- Cary and Blair medium for preserving enteric pathogens