Culture media

Culture media

Culture media: Can be defined as an artificially prepared substance containing various microbial nutritional requirements of optimum pH which will allow the growth of most microorganisms.
Classification of culture media:
* According to consistency (hradness), culture media can be classified into liquid media, semi solid media and solid media.
(A) Liquid media:
Are used for particular biochemical tests, sensitivity tests. It has some disadvantages:
- Growth usually do not exhibit special characteristic appearance.
- When there is more than one type of organisms they can not be separated by growing in liquid media.
(B) Semi solid media:
Its use to separate a mixture of a motile and non motile organisms (contain 0.2-0.5% agar).
(C) Solid media: Contain 2.-3% agar.
Agar-ager: it is long chain polysaccharide containing inorganic salts and a small amount of proteins. It act as a solidifying agent and solidify only when cooled to 42?C.
Solid media has some special advantages:
(1) Growth usually shows special characteristic appearance that helps in identification of the organisms.
(2) Microorganisms can be separated with certainly from mixtures by growth fall in a solid media.
* According to composition, nutritional media divided into two types:
a) Basic or simple media: This type of media contains only the basic requirement for the growth of bacteria like sources of carbon, nitrogen, energy, e.g. nutrient agar, nutrient broth and peptone water.
b) Special media: Which provide specific requirements that may include inorganic salts.
(1) Enriched media: The media is enriched by addition of extra growth factors like egg, serum, blood, e.g. blood agar (use to detect hemolytic activity of bacteria), chocolate agar (when blood agar heated to 80?C for 10 min., the media change to a chocolate brown color).
(2) Selective media: They are solid media in which some special substances are incorporated which will allow the growth of some bacteria and prevent the others.