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culture media

الكلية كلية الهندسة     القسم  الهندسة البيئية     المرحلة 1
أستاذ المادة اشواق مخيف سلمان حبيب الجبوري       11/07/2018 19:42:25
culture media
iculture media
is a liquid or gel designed to support the growth of microorganisms or cells. There are different types of media for growing different types of cells.
An important distinction between growth media types is that of defined versus undefined media. A defined medium will have known quantities of all ingredients. For microorganisms, they consist of providing trace elements and vitamins required by the microbe and especially a defined carbon source and nitrogen source. Glucose or glycerol are often used as carbon sources, and ammoniumsalts or nitrates as inorganic nitrogen sources. An undefined medium has some complex ingredients, such as yeast extract or casein hydrolysate, which consist of a mixture of many, many chemical species in unknown proportions. Undefined media are sometimes chosen based on price and sometimes by necessity – some microorganisms have never been cultured on defined media.

Types of culture media
Media are of different types on consistency and chemical composition.

A. On Consistency:
1. Solid Media. Advantages of solid media:
(a) Bacteria may be identified by studying the colony character
1. BasalMedia. Basal media are those that may be used for growth (culture) of bacteria that do not need enrichment of the media. Examples: Nutrient broth, nutrient agar and peptone water. Staphylococcus and Enterobacteriaceae grow in these media.

2. EnrichedMedia. The media are enriched usually by adding blood, serum or egg. Examples: Enriched media are blood agar and Lowenstein-Jensen media. Streptococci grow in blood agar media.

3. SelectiveMedia. These media favors the growth of a particular bacterium by inhibiting the growth of undesired bacteria and allowing growth of desirable bacteria. Examples: MacConkey agar, Lowenstein-Jensen media, tellurite media (Tellurite inhibits the growth of most of the throat organisms except diphtheria bacilli). Antibiotic may be added to a medium for inhibition.

4. Indicator (Differential) Media An indicator is included in the medium. A particular organism causes change in the indicator, e.g. blood, neutral red, tellurite. Examples: Blood agar and MacConkey agar are indicator media.
5. TransportMedia. These media are used when specie-men cannot be cultured soon after collection. Examples: Cary-Blair medium, Amies medium, Stuart medium.
(b) Mixed bacteria can be separated.
Solid media is used for the isolation of bacteria as pure culture. Agar is most commonly used to prepare solid media. Agar is polysaccharide extract obtained from seaweed. Agar is an ideal solidifying agent as it is :
(a) Bacteriologically inert, i.e. no influence on bacterial growth
(b) It remains solid at 37°C
(c) It is transparent.
2. Liquid Media. It is used for profuse growth, e.g. blood culture in liquid media. Mixed organisms cannot be separated.

B. On Chemical Composition :
1. Routine Laboratory Media
2. Synthetic Media. These are chemically defined media prepared from pure chemical substances. It is used in research work.
RoutineLaboratoryMedia
These are classified into six types:
(1) Basal media, (2) Enriched media, (3) Selective media, (4) Indicator media, (5) Transport media, and (6) Storage media.


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