The common ingredients found in culture media are agar,peptone,meat extracts,yeast extract,carbohydrates,mineral salts,buffers,pH indicators and water.
Culture media can be classified on the basis of chemical composition,use and physical state.
On the basis of physical state
Major solidifying agent is in solid state that contains agar.These media contains 1.5% agar.this form of media is mainly used in Petri dishes as plate cultures.They are used to observe the colony characteristics,size,shape of microorganisms and also for the isolation and enumeration.e.g.MacConkey agar,blood agar,etc.
These media are gelatinous in nature with jelly like consistency.These are prepared by adding 0.2-0.5%agar to a fluid medium.These media are used for motility test and for different biochemical test.e.g.SIM media,Hugh and Leifson’s media.
It does not contain any solidifying agent or any agar.growth of the organisms are shown by the turbidity in the medium.Generally,liquid media are used for the propagation of a large number of microorganisms,for the transfer of microorganisms.e.g.peptone water,MacConkey broth,nutrient broth etc.
On the basis of chemical composition
Those media whose chemical composition is not known are called natural media.It contain all necessary ingredients for growth of microorganisms,but they are in crude form.They are more useful for cultivating unknown bacteria,as it usually provides full range of growing factors such as amino acids,polypeptides,vitamins and minerals.
Media prepared by adding precise amount of highly purified inorganic or organic chemicals to distilled water are synthetic media.So chemical composition is known in this media.This media are of great importance in studying the metabolic activity of microorganisms.Examples include enrichment media,Czapek and Richard’solution.
The media of which chemical composition is partially known is as semisynthetic media.e.g.nutreint agar,PDA,Czapek Dox agar,etc.
On the basis of utility purpose
General purpose media
Enrichment media &transport media