Microbial Culture Media
For the growth of microorganism in invitro conditions a suitable medium is necessary. So for the growth of microorganisms in any artificial condition, a liquid, semi solid or solid medium is designed to support the growth of microorganisms and the medium is known as microbial culture medium.
There were different classification of microbial culture medium:-
1.Based on the concentration of solidifying agent used in the culture medium.
2.Based on their Oxygen demand.
3.Based on the ingredients used in the medium
Table of Content
2.Based on their Oxygen demand.
3.Based on the ingredients used in the medium
1. Based on the concentration of solidifying agent used in the culture medium.
The microbial culture is again classified in to three, based on the concentration of agar agar.
a) Solid medium
Here, 2% of agar concentration is used. By using the above culture medium, bacteria can be identified easily. One of the disadvantage of using this media was that it takes 24 hours for the growth of bacteria. Example:- Chochlate agar ( the name is due to its colour. No chocolate is used in this medium)
Blood:- sheep blood is used in this medium. Red blood cells will lysed on slow heating.)
b) Liquid medium ( media with broth or water)
In this medium, agar is not used and so it remain liquid . Growth appears in 4 hours. It promote the growth of many bacteria. Example:- Peptone broth, Nutrient broth.
C) Semi solid medium
Here, 0,2 % to 0.5 % of agar agar powder concentration is used. This culture medium is useful to check the motility of bacteria.
2. Based on the Oxygen demand
On their prerequisite for oxygen, the medium is also classified in to two:- Aerobic medium and Anaerobic medium.
a) Aerobic medium :- The growth of bacteria takes place in the presence of Oxygen.
b) Anaerobic medium :- this particular culture medium is used for the bacteria which can not flourish in the presence of Oxygen. Example :- REM Media ( Robertson Cooked Meat Broth). The meat particles present in the medium utilize the oxygen and thereby creates an anaerobic environment for the growth of bacteria.
3. Based on the ingredients used in the medium
a) Simple media :- Contain simple or basic ingredients in the medium. Example:- Nutrient broth.
b) Complex media / Undefined media :- The medium is highly nutritious. They contain water soluble extracts of enzymatically digested animal protein such as peptone or tryptone. Exact composition of the medium is not known. Yeast extracts, casein hydrolysate were added. It consists of many ingredients of unknown proportions. Carbon source were also added.
Extra nutrient substances were added to the simple media results in complex media. Example :- Blood Agar.
c) Defined media / Synthetic media :- The medium is chemically defined. It consist of ingredients ( chemicals) of known quantities. ie, the exact composition of medium is known. Here, animal tissues or plant products or yeast is not used. It is the purest and most consistent culture medium used for the animal cell culture. Double distilled water is used for the preparation of media. The ingredients were measured and dissolved in the double distilled water. Carbon source like glucose or glycerol were provided. Ammonium salts or nitrates were used as nitrogen source. Trace elements and vitamins were also supplied.
d) Semi defined media :- Appropriate concentration of ingredients were used, the concentration is exactly not known.
e) Special media :- Special media is further classified as
a) Enrichment media :- Basically, liquid in nature. This culture media contain enrichment substances or have inhibitory substances, which helps to slow down the growth of unwanted bacteria and permits the growth of certain bacteria.
Example :- tetrathionate broth, which contain inhibitory substances. Bile salt inhibit the growth of coliform and gram negative bacteria but favors salmonella
b) Enrich media :- for the enhanced growth of micro organisms blood or serum or egg were added in to the basal medium. It is rich in nutrients.
c) Selective media :- selective media is used for the growth of selected microorganisms only. The selective media used for the growth of eukaryotic cells contain neomycin. Certain antibiotics like tetracyclin or ampicillin were added to the medium contain microorganisms which resist this antibiotics and there by prevent other cells which do not posses this resistance.
Example :- Eosin methylene blue (EMB) - it contain methylene blue and they are toxic to the gram positive bacteria. Hence only the growth of gram negative bacteria will be allowed.
Mannitol Salt sugar – presence of high sodium chloride concentration inhibit the growth of most organisms but favours the growth of staphylococcus
d) Differential media / Indicator media :- this type of medium contain special type of ingredients, which allows particular groups of microorganisms to be visually distinguished from one another. Certain dyes or chemicals present in the medium produce characteristic growth patterns that were used for the identification.
e) Transport media :- this type of medium is used to transport the organisms from their collecting area to the laboratory. The media contains buffers and non nutritional substances, which prevent the unwanted growth of microorganisms.
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