Culture media or growth media are solid, liquid or semi-solid substances that aid in the proliferation of bacterial populations. Here, let’s see the different types of culture media with examples.
Table of Contents
- What is Culture Media
- Simple Media
- Complex Media
- Synthetic Media
- Special Media
- Frequently Asked Questions
What is Culture Media?
Culture media is a gel or liquid that contains nutrients and is used to grow bacteria or microorganisms. They are also termed growth media. Different cell types are grown in various types of medium. Nutrient broths and agar plates are the most typical growth media for microorganisms. Some microorganisms or bacteria need special media for their growth.
Significance – Culture media is used in order to identify the causative agent from infected material.
Types of Culture Media
The culture media are classified in many different ways:
- Based on the physical state
- Liquid media
- Solid media
- Semisolid media
- Anaerobic media
- Aerobic media
- Simple media
- Synthetic media
- Complex media
- Special media
Nutrient broths or lysogeny broth (LB) medium are the two most popular growth media for bacteria. Agar is frequently added to liquid media before being placed into a petri dish to solidify. These agar plates offer a stable medium for the cultivation of bacteria. It stays solid because relatively few bacteria can break down agar.
Simple culture media includes nutrient broth. One percent meat extract and peptone water makes up such broth. Nutrient broth becomes glucose broth when glucose is added to it. Likewise, it becomes nutrient agar when 2-3% agar is added. For purposes of diagnosis, this is the simplest and most common media used in laboratories. A semisolid medium that permits the propagation of motile bacteria can be produced if the concentration of agar is decreased. Examples – peptone water, nutrient agar and glucose broth.
Other than simple media, all forms of media are termed complex media. Complex media contain additional components for bringing out specific qualities or providing the unique nutrients needed for the bacterium’s growth. Here, the source of the amino acids contains a variety of chemicals whose precise composition is unknown, thus it is an undefinable media. Examples – MacConkey agar medium and chocolate agar.
A synthetic medium is a defined medium. A defined medium (chemically defined medium) is a medium in which there is no yeast, plant or animal tissue present, and all the chemicals employed are known. These are made from only pure ingredients whose exact composition is known. These are employed in specialised investigations like those on metabolic needs. Example – Dubo’s culture medium with tween 80.
Also Check: Plant Tissue Culture
Special media are of seven different types:
- Enriched media – It is created when a basic medium is supplemented with nutrients like eggs, blood or serum. For example, a blood agar medium is used for the growth of bacteria like Streptococcus which specifically requires blood for its proliferation.
- Selective media – Selective media contain components that prevent the growth of all but a small number of bacterial species and make it easier to isolate a specific species. When mixed bacterial flora is anticipated in specimens, these media are utilised to isolate specific bacteria from those specimens. For example, bile salt acts as a selective agent in BSA or bile salt agar. While preventing the growth of other intestinal organisms, it favours the growth of Vibrio cholerae.
- Differential media – It is a term used to describe a medium that has components that aid in identifying the various properties of bacteria. Peptone, agar, lactose, neutral red and sodium taurocholate are all ingredients in MacConkey’s medium. Here, the colonies made by lactose fermenters are pink, but those made by non-lactose fermenters are pale or colourless.
- Enrichment media – This media contains several ingredients that either stimulate the bacteria being grown or suppress their competitors. Examples – Alkaline peptone water and tetrathionate broth.
- Transport media – These are employed when dealing with delicate organisms that might not make it through the transit period or might become covered with non-pathogenic germs. Special media are developed for the transportation of such bacteria to laboratories and these are known as transport media. Example – Stuart’s transport medium.
- Indicator media – When bacteria multiply in these media containing an indicator, they tend to change their colour. MacConkey’s medium is also an example of an indicator medium. Another classic example is the black colonies of Salmonella typhi that develop on sulphite-containing Wilson and Blair media.
- Sugar media – It contains 1% sugar, which can be any fermentable substance like glucose, mannitol, sucrose and lactose. The generation of acid following the fermentation of sugar transforms the medium into pink due to the presence of an indicator. Also to show that gas is produced, Durham’s tube is kept inverted inside the sugar tube and gas bubbles are observed.
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