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A growth medium or culture medium is a solid, liquid or semi-solid designed to support the growth of microorganisms or cells,[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 cell culture, which use specific cell types derived from plants or animals, and microbiological culture, which are used for growing microorganisms, such as bacteria or fungi. The most common growth media for microorganisms are nutrient broths and agar plates; specialized media are sometimes required for microorganism and cell culture growth.[1] Some organisms, termed fastidious organisms, require specialized environments due to complex nutritional requirements. Viruses, for example, are obligate intracellular parasites and require a growth medium containing living cells.

Contents

1 Types

1.1 Culture media 1.2 Minimal media 1.3 Selective media 1.4 Differential media 1.5 Transport media

2 Enriched media 3 See also 4 References 5 External links

Types[edit] The most common growth media for microorganisms are nutrient broths (liquid nutrient medium) or LB medium (lysogeny broth). 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
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, hormones or growth factors which usually occur in vivo.[6] In the case of animal cells, this difficulty is often addressed by the addition of blood serum or a synthetic serum replacement to the medium. In the case of microorganisms, no such limitations exist, as they are often unicellular organisms. One other major difference is that animal cells in culture are often grown on a flat surface to which they attach, and the medium is provided in a liquid form, which covers the cells. In contrast, bacteria such as Escherichia coli
Escherichia coli
may be grown on solid or in liquid media. An important distinction between growth media types is that of defined versus undefined media.[1] 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 defined carbon and nitrogen sources. Glucose
Glucose
or glycerol are often used as carbon sources, and ammonium salts 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 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. A good example of a growth medium is the wort used to make beer. The wort contains all the nutrients required for yeast growth, and under anaerobic conditions, alcohol is produced. When the fermentation process is complete, the combination of medium and dormant microbes, now beer, is ready for consumption. The main types are

Cultural media Minimal media Selective media Differential media Transport media Indicator media

Culture media[edit] 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.

Physcomitrella patens
Physcomitrella patens
plants growing axenically on agar plates (Petri dish, 9 cm diameter)

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 with the exact composition being 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

Some examples of nutrient media include:

Plate count agar Nutrient agar Trypticase soy agar

Minimal media[edit] Minimal media are those that contain the minimum nutrients possible for colony growth, generally without the presence of amino acids, and are often used by microbiologists and geneticists to grow "wild-type" microorganisms. Minimal media can also be used to select for or against recombinants or exconjugants. 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 auxotrophic recombinants. Selective media[edit]

Blood-free, charcoal-based selective medium agar (CSM) for isolation of Campylobacter

Blood agar
Blood agar
plates are often used to diagnose infection. On the right is a positive Streptococcus
Streptococcus
culture; on the left is a positive Staphylococcus
Staphylococcus
culture.

Selective media are used for the growth of only selected microorganisms. For example, if a microorganism is resistant to a certain antibiotic, such as ampicillin or tetracycline, then that antibiotic can be added to the medium to prevent other cells, which do not possess the resistance, from growing. Media lacking an amino acid such as proline in conjunction with E. coli unable to synthesize it were commonly used by geneticists before the emergence of genomics to map bacterial chromosomes. Selective growth media are also used in cell culture to ensure the survival or proliferation of cells with certain properties, such as antibiotic resistance or the ability to synthesize a certain metabolite. Normally, the presence of a specific gene or an allele of a gene confers upon the cell the ability to grow in the selective medium. In such cases, the gene is termed a marker. Selective growth media for eukaryotic cells commonly contain neomycin to select cells that have been successfully transfected with a plasmid carrying the neomycin resistance gene as a marker. Gancyclovir
Gancyclovir
is an exception to the rule, as it is used to specifically kill cells that carry its respective marker, the Herpes simplex virus
Herpes simplex virus
thymidine kinase (HSV TK).

Four types of agar plate demonstrating differential growth depending on bacterial metabolism

Examples of selective media include:

Eosin methylene blue
Eosin methylene blue
contains dyes that are toxic for Gram-positive bacteria. It is the selective and differential medium for coliforms. YM (yeast extract, malt extract agar) has a low pH, deterring bacterial growth. MacConkey agar
MacConkey agar
is for Gram-negative
Gram-negative
bacteria. Hektoen enteric agar is selective for Gram-negative
Gram-negative
bacteria. Mannitol salt agar
Mannitol salt agar
is selective for Gram-positive bacteria
Gram-positive bacteria
and differential for mannitol. Xylose lysine deoxycholate is selective for Gram-negative
Gram-negative
bacteria. Buffered charcoal yeast extract agar is selective for certain Gram-negative
Gram-negative
bacteria, especially Legionella pneumophila. Baird–Parker agar is for Gram-positive staphylococci. Sabouraud's agar
Sabouraud's agar
is selective to certain fungi due to its low pH(5.6) and high glucose concentration(3-4%)

Differential media[edit] Differential or indicator media distinguish one microorganism type from another growing on the same medium.[7] 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 include:

Blood agar
Blood agar
(used in strep tests) contains bovine heart blood that becomes transparent in the presence of β-hemolytic organisms such as Streptococcus
Streptococcus
pyogenes and Staphylococcus
Staphylococcus
aureus. Eosin methylene blue
Eosin methylene blue
is differential for lactose fermentation. Granada medium
Granada medium
is selective and differential for Streptococcus agalactiae (group B streptococcus) which grows as distinctive red colonies in this medium. MacConkey agar
MacConkey agar
is differential for lactose fermentation. Mannitol salt agar
Mannitol salt agar
is differential for mannitol fermentation. X-gal
X-gal
plates are differential for lac operon mutants.

Transport media[edit] 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 include:

Thioglycolate broth
Thioglycolate broth
is for strict anaerobes. Stuart transport medium 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[edit] 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. Blood agar
Blood agar
is an enriched medium in which nutritionally rich whole blood supplements the basic nutrients. Chocolate agar
Chocolate agar
is enriched with heat-treated blood (40–45 °C), which turns brown and gives the medium the color for which it is named. See also[edit]

Cell culture Impedance microbiology Modified Chee's medium

References[edit]

^ a b c Madigan M, Martinko J, eds. (2005). Brock Biology of Microorganisms (11th ed.). Prentice Hall. ISBN 0-13-144329-1.  ^ Birgit Hadeler, Sirkka Scholz, Ralf Reski
Ralf Reski
(1995) Gelrite and agar differently influence cytokinin-sensitivity of a moss. Journal of Plant
Plant
Physiology 146, 369–371 ^ Ryan KJ, Ray CG, eds. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 0-8385-8529-9.  ^ Hans Günter Schlegel (1993). General Microbiology. Cambridge University. p. 459. ISBN 978-0-521-43980-0. Retrieved 6 August 2013.  ^ Parija, Shubhash Chandra (1 January 2009). Textbook of Microbiology & Immunology. Elsevier India. p. 45. ISBN 978-81-312-2163-1. Retrieved 6 August 2013.  ^ Cooper GM (2000). "Tools of Cell Biology". The cell: a molecular approach. Washington, D.C: ASM Press. ISBN 0-87893-106-6.  ^ Washington JA (1996). "Principles of Diagnosis". In Baron S; et al. Baron's Medical Microbiology (4th ed.). Univ of Texas Medical Branch. ISBN 0-9631172-1-1. 

External links[edit]

The Nutrient Requirements of Cells

v t e

Growth media / agar plates

Selective media

Gram positive

Actinobacteria

Mycobacterium tuberculosis

Löwenstein–Jensen medium Middlebrook 7H9 Broth Middlebrook 7H10 Agar Middlebrook 7H11 Agar

Mycoplasma pneumoniae

Eaton's agar

Firmicutes

Corynebacterium diphtheriae

Hoyle's agar

Enterococcus

Bile esculin agar

Lactobacillus

MRS agar

Lactococcus

M17 agar

Staphylococcus

Mannitol salt agar

Gram negative

Alphaproteobacteria

Brucella

Brucella
Brucella
agar Farrell's medium

Betaproteobacteria

Neisseria

Thayer-Martin agar

Gammaproteobacteria

Bordetella

Bordet-Gengou agar

Enterobacteriaceae

VRBD agar

Haemophilus influenzae/Legionella pneumophila

Buffered charcoal yeast extract agar

Pseudomonas
Pseudomonas
aeruginosa

Cetrimide agar

Salmonella

XLT agar

DCA agar Salmonella/Shigella

XLD agar

Differential media

Lactose
Lactose
fermenting gram negative

MacConkey agar/Sorbitol-MacConkey agar Eosin
Eosin
methylene blue

Hektoen enteric agar sulfur

Bismuth sulfite agar

Fungal media

Czapek medium Dermatophyte test medium Potato dextrose agar Sabouraud agar

Nonselective media

Chocolate agar Nutrient agar Plate count agar

Other/ungrouped media

Cystine lactose electrolyte deficient agar Cystine tryptic agar Endo agar Lysine iron agar slant Müller-Hinton agar/PNP agar R2a agar Simmons' citrate agar Trypticase soy agar Tryptic soy broth TSI slant

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