Growth medium
A growth medium or culture medium is a solid, liquid, or semi-solid designed to support the growth of a population of microorganisms or cells via the process of cell proliferation[1] or small plants like the moss Physcomitrella patens.[2] Different types of media are used for growing different types of cells.[3]
The two major types of growth media are those used for
Types
The most common growth media for microorganisms are nutrient broths (liquid nutrient medium) or lysogeny broth medium. Liquid media are often mixed with agar and poured via a sterile media dispenser into Petri dishes to solidify. These agar plates provide a solid medium on which microbes may be cultured. They remain solid, as very few bacteria are able to decompose agar (the exception being some species in the genera: Cytophaga, Flavobacterium, Bacillus, Pseudomonas, and Alcaligenes). Bacteria grown in liquid cultures often form colloidal suspensions.[4][5]
The difference between growth media used for cell culture and those used for microbiological culture is that cells derived from whole organisms and grown in culture often cannot grow without the addition of, for instance,
An important distinction between growth media types is that of
A good example of a growth medium is the
- culture media
- minimal media
- selective media
- differential media
- transport media
- indicator media
Culture media
Culture media contain all the elements that most bacteria need for growth and are not selective, so they are used for the general cultivation and maintenance of bacteria kept in laboratory culture collections.
An undefined medium (also known as a basal or complex medium) contains:
- a carbon source such as glucose
- water
- various salts
- a source of amino acids and nitrogen (e.g. beef, yeast extract)
This is an undefined medium because the amino-acid source contains a variety of compounds; the exact composition is unknown.
A defined medium (also known as chemically defined medium or synthetic medium) is a medium in which
- all the chemicals used are known
- no yeast, animal, or plant tissue is present
Examples of nutrient media:
Minimal media
A defined medium that has just enough ingredients to support growth is called a "minimal medium". The number of ingredients that must be added to a minimal medium varies enormously depending on which microorganism is being grown.
Minimal medium typically contains:
- a carbon source, which may be a sugar such as glucose, or a less energy-rich source such as succinate
- various salts, which may vary among bacteria species and growing conditions; these generally provide essential elements such as magnesium, nitrogen, phosphorus, and sulfur to allow the bacteria to synthesize protein and nucleic acids
- water
Supplementary minimal media are minimal media that also contains a single selected agent, usually an amino acid or a sugar. This supplementation allows for the culturing of specific lines of
Selective media
Selective media are used for the growth of only selected microorganisms. For example, if a microorganism is resistant to a certain
Selective growth media are also used in
Selective growth media for
Examples of selective media:
- Eosin methylene blue contains dyes that are toxic for Gram-positive bacteria. It is the selective and differential medium for coliforms.
- YM (yeast extract agar) has a low pH, deterring bacterial growth.
- MEA (malt extract agar) has a low pH, deterring bacterial growth.
- Gram-negativebacteria.
- Hektoen enteric agar is selective for Gram-negative bacteria.
- HIS-selective medium is a type cell culture medium that lacks the amino acid histidine.
- Mannitol salt agar is selective for gram-positive bacteria and differential for mannitol.
- Xylose lysine deoxycholate is selective for Gram-negative bacteria.
- Buffered charcoal yeast extract agar is selective for certain gram-negative bacteria, especially Legionella pneumophila.
- staphylococci.
- Sabouraud agar is selective to certain fungi due to its low pH (5.6) and high glucose concentration (3–4%).
- DRBC (dichloran rose bengal chloramphenicol agar) is a selective medium for the enumeration of moulds and yeasts in foods. Dichloran and rose bengal restrict the growth of mould colonies, preventing overgrowth of luxuriant species and assisting accurate counting of colonies.[8]
Differential media
Differential or indicator media distinguish one microorganism type from another growing on the same medium.[11] This type of media uses the biochemical characteristics of a microorganism growing in the presence of specific nutrients or indicators (such as neutral red, phenol red, eosin y, or methylene blue) added to the medium to visibly indicate the defining characteristics of a microorganism. These media are used for the detection of microorganisms and by molecular biologists to detect recombinant strains of bacteria.
Examples of differential media:
- Blood agar (used in strep tests) contains bovine heart blood that becomes transparent in the presence of β-hemolytic organisms such as Streptococcus pyogenes and Staphylococcus aureus.
- Eosin methylene blue is differential for lactose fermentation.
- Granada medium is selective and differential for Streptococcus agalactiae (group B streptococcus) which grows as distinctive red colonies in this medium.
- MacConkey agar is differential for lactose fermentation.
- Mannitol salt agar is differential for mannitol fermentation.
- X-gal plates are differential for lac operon mutants.
Transport media
Transport media should fulfill these criteria:
- Temporary storage of specimens being transported to the laboratory for cultivation
- Maintain the viability of all organisms in the specimen without altering their concentration
- Contain only buffers and salt
- Lack of carbon, nitrogen, and organic growth factors so as to prevent microbial multiplication
- Transport media used in the isolation of anaerobes must be free of molecular oxygen.
Examples of transport media:
- Thioglycolate broth is for strict anaerobes.
- Stuart transport medium[12][13] is a non-nutrient soft agar gel containing a reducing agent to prevent oxidation, and charcoal to neutralize.
- Certain bacterial inhibitors are used for gonococci, and buffered glycerol saline for enteric bacilli.
- Venkataraman Ramakrishna (VR) medium is used for V. cholerae.
Enriched media
Enriched media contain the nutrients required to support the growth of a wide variety of organisms, including some of the more fastidious ones. They are commonly used to harvest as many different types of microbes as are present in the specimen.
Physiological relevance
The choice of culture medium might affect the
See also
References
- ^ ISBN 0-13-144329-1.
- ^ Birgit Hadeler; Sirkka Scholz; Ralf Reski (1995). "Gelrite and agar differently influence cytokinin-sensitivity of a moss". Journal of Plant Physiology (146): 369–371.
- ISBN 0-8385-8529-9.
- ISBN 978-0-521-43980-0. Retrieved 6 August 2013.
- ISBN 978-81-312-2163-1. Retrieved 6 August 2013.
- ISBN 0-87893-106-6.
- ^ Catherine A. Ingraham, John L. Ingraham (2000). Introduction to Microbiology.
- ISBN 978-0-444-81498-2. Retrieved 2020-04-20.
- .
- ^ Chaitali Bhattacharya; Alok Adholeya. "Showcasing Ectomycorrhizal Culture". bookstore.teri.res.in. Retrieved 2023-02-04.
- ISBN 0-9631172-1-1.
- ISBN 978-4-431-70313-6, retrieved 2023-09-07
- ^ Smriti, Saifun Nahar (2023-09-07). "Culture media: Definition, Types and Preparation Methods". GreenLeen.Com. Retrieved 2023-09-07.
- ^ "Enrichment Culture - an overview". ScienceDirect Topics. Retrieved 2023-09-07.
- S2CID 222319735.)
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: CS1 maint: multiple names: authors list (link - PMID 31039782.
- PMID 30613774.
- PMID 28388410.)
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