Culture Media
A substance used to provide nutrients for growth and multiplication of microorganisms is called culture media.
Colonization of bacteria occurs in culture media.
1. Colony
Macroscopically (with nacked eye) visible growth of microorganisms on solid culture medium.
2. Culturing/Colonization
It is process of growing bacterial colonies in an artificial medium containing all suitable nutrients and favourable conditions.
Types of culture media
1. On the basis of consistency media are;
1. Liquid media
2. Semi liquid medium
3. Solid media
1. Liquid media
Solid agent agar-agar absent, so it called broth.
Infusion broth
Meat extract broth
Bile broth
Liquid media used for;
Preparing bulk culture of antigen or vaccines
For biochemical test
Antibiotic sensitivity test
Observe motility of bacteria
2. Semi solid medium
Prepared with solidfying agent agar.
These medium have soft and gel like;
Gelatin
Serum
Egg media
Semi solid medium useful for;
Cultivation of microaerophilic bacteria
For determination of bacterial motility
3. Solid media
It is prepared with agar-agar (solidfying agent).
Solid media are;
Natural agar
Blood agar medium
Solid media useful for;
Isolating bacteria from impure/mixed culture.
Determining characteristics of colonies.
2. In the based on nature of constituent culture media are;
1. Simple or basal media
Certain and basic ingredients of all media such as; peptone water and nutrient broth are liquid basal media but nutrient agar is solid basal media.
2. Synthetic media/ define media
Prepared from pure chemical substance and their exact composition is known.
3. Non synthetic/ complex media
Ingredients are added to bringing out certain characteristics of bacteria or providing specific nutrient for growth of bacteria.
3. Classification based on application or function
Special media are;
1. Enriched media
2. Selective media
3. Sugar media
4. Transportation media
5. Anaerobic media
6. Indicator media
7. Differential media
1. Enriched media
When basal solid medium (nutrient agar) is added with some nutrients substance such as;
Blood
Serum or egg
Used to promote non-selective growth of any bacteria that may be present.
2. Selective Media
In this medium inhibitory substance added to solid medium which help to grow required bacterium to form colonies and inhibit other underused bacteria.
3. Indicator media
These media contain an indicator which changes colour when bacterium grows in them.
For example; Diphtheria bacillus produce black colonies on Mcleod medium.
4. Differential media
A media which certain substance that enables it to bring out differential characteristic of bacteria. So it is called differential media.
For example;
MacConkey's medium, contains lactose- bacteria grow on it- lactose fermenting - bacteria show pink colour colonies.
Blood agar medium helps to differentiate between Haemolytic and non- hemolytic bacteria.
5. Sugar media
Presence of sugar in medium is used to detect presence of any fermentable bacteria in medium.
6. Transport media
7. Anaerobic media
These media are used for growing anaerobic organisms.
For example;
Robertson's cooked meat medium
8. Stroage media
In such media, bacteria are stored as stock cultures for longer period of time.
Bacterial cultures are preserved and stored in such media by freeze -day method.
0 Comments