Agar plate
Encyclopedia
An agar plate is a Petri dish
that contains a growth medium
(typically agar
plus nutrients) used to culture
microorganisms or small plants like the moss
Physcomitrella patens
.
Selective growth compounds may also be added to the media, such as antibiotic
s.
Individual microorganisms placed on the plate will grow into individual colonies
, each a clone
genetically identical to the individual ancestor organism (except for the low, unavoidable rate of mutation
). Thus, the plate can be used either to estimate the concentration of organisms in a liquid culture
or a suitable dilution of that culture using a colony counter
, or to generate genetically pure cultures from a mixed culture of genetically different organisms, using a technique known as "streaking
". In this technique, a drop of the culture on the end of a thin, sterile
loop of wire, sometimes known as an inoculator, is streaked across the surface of the agar leaving organisms behind, a higher number at the beginning of the streak and a lower number at the end. At some point during a successful "streak", the number of organisms deposited will be such that distinct individual colonies will grow in that area which may be removed for further culturing, using another sterile loop.
, suggested agar as an effective setting agent since it had been common place in jam making for some time.
Like other growth media
, the formulations of agar used in plates may be classified as either "defined" or "undefined"; defined medium is synthesized from individual chemicals required by the organism so that the exact molecular composition is known, whereas undefined medium is made from natural products such as yeast extract
, where the precise composition is unknown.
Agar plates may be formulated as either permissive, with the intent of allowing the growth of whatever organisms are present, or restrictive or selective, with the intent of only allowing growth a particular subset of those organisms. This may take the form of a nutritional requirement, for instance providing a particular compound such as lactose
as the only source of carbon
and thereby selecting only organisms which can metabolize
that compound, or by including a particular antibiotic or other substance in order to select only organisms which are resistant
to that substance. This correlates to some degree with defined and undefined media; undefined media, made from natural products and containing an unknown combination of very many organic molecules, is typically more permissive in terms of supplying the needs of a wider variety of organisms, while defined media can be precisely tailored to select organisms with specific properties.
Agar plates may also be indicator plates, in which the organisms are not selected on the basis of growth, but are instead distinguished by a color change in some colonies, typically caused by the action of an enzyme
on some compound added to the media.
Some commonly used agar plate types are:
Blood agar plate (BAP)
Blood agar plate (BAP) Contains mammalian blood (usually sheep or horse), typically at a concentration of 5–10%. BAP are enriched, differential media used to isolate fastidious
organisms and detect hemolytic
activity. β-hemolytic activity will show lysis and complete digestion of red blood cell contents surrounding colony. Examples include Streptococcus haemolyticus. α-hemolysis will only partially lyse (the cells are either lysed or not- it is the digestion that may be incomplete) the hemoglobin and will appear green. An example of this would be Streptococcus viridans. γ-hemolysis (or non-hemolytic) is the term referring to a lack of hemolytic activity.
Contains meat extract, tryptone
, sodium chloride
, and agar.
Chocolate agar
Chocolate agar
(CHOC) is a type of blood agar plate in which the blood cells have been lysed
by heating the cells to 56 °C. Chocolate agar is used for growing fastidious (fussy) respiratory bacteria, such as Haemophilus influenzae
. No chocolate
is actually contained in the plate; it is named for the coloration only.
Horse blood agar
Horse blood agar (HBA
) is a type of blood enriched microbiological culture media. As it is enriched, it allows the growth of certain fastidious bacteria, and allows indication of haemolytic activity in these bacterial cultures.
Thayer-Martin agar
Thayer-Martin agar
(TM) is a chocolate agar designed to isolate Neisseria gonorrhoeae
.
Thiosulfate-citrate-bile salts-sucrose agar
Thiosulfate-citrate-bile salts-sucrose agar (TCBS) enhances growth of Vibrio spp.
, including Vibrio cholerae
Petri dish
A Petri dish is a shallow glass or plastic cylindrical lidded dish that biologists use to culture cells or small moss plants. It was named after German bacteriologist Julius Richard Petri, who invented it when working as an assistant to Robert Koch...
that contains a growth medium
Growth medium
A growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens.There are different types of media for growing different types of cells....
(typically agar
Agar
Agar or agar-agar is a gelatinous substance derived from a polysaccharide that accumulates in the cell walls of agarophyte red algae. Throughout history into modern times, agar has been chiefly used as an ingredient in desserts throughout Asia and also as a solid substrate to contain culture medium...
plus nutrients) used to culture
Microbiological culture
A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested,...
microorganisms or small plants like the moss
Moss
Mosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
Physcomitrella patens
Physcomitrella patens
Physcomitrella patens is a moss used as a model organism for studies on plant evolution, development and physiology.-Model organism:...
.
Selective growth compounds may also be added to the media, such as antibiotic
Antibiotic
An antibacterial is a compound or substance that kills or slows down the growth of bacteria.The term is often used synonymously with the term antibiotic; today, however, with increased knowledge of the causative agents of various infectious diseases, antibiotic has come to denote a broader range of...
s.
Individual microorganisms placed on the plate will grow into individual colonies
Colony (biology)
In biology, a colony reference to several individual organisms of the same species living closely together, usually for mutual benefit, such as stronger defense or the ability to attack bigger prey. Some insects live only in colonies...
, each a clone
Cloning
Cloning in biology is the process of producing similar populations of genetically identical individuals that occurs in nature when organisms such as bacteria, insects or plants reproduce asexually. Cloning in biotechnology refers to processes used to create copies of DNA fragments , cells , or...
genetically identical to the individual ancestor organism (except for the low, unavoidable rate of mutation
Mutation
In molecular biology and genetics, mutations are changes in a genomic sequence: the DNA sequence of a cell's genome or the DNA or RNA sequence of a virus. They can be defined as sudden and spontaneous changes in the cell. Mutations are caused by radiation, viruses, transposons and mutagenic...
). Thus, the plate can be used either to estimate the concentration of organisms in a liquid culture
Microbiological culture
A microbiological culture, or microbial culture, is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. Microbial cultures are used to determine the type of organism, its abundance in the sample being tested,...
or a suitable dilution of that culture using a colony counter
Colony counter
A colony counter is an instrument used to count colonies of bacteria or other microorganisms growing on an agar plate. Early counters were merely lighted surfaces on which the plate was placed, with the colonies marked off with a felt-tipped pen on the outer surface of the plate while the operator...
, or to generate genetically pure cultures from a mixed culture of genetically different organisms, using a technique known as "streaking
Streaking (microbiology)
In microbiology, Streaking is a technique used to isolate a pure strain from a single species of microorganism, often bacteria. Samples can then be taken from the resulting colonies and a microbiological culture can be grown on a new plate so that the organism can be identified, studied, or...
". In this technique, a drop of the culture on the end of a thin, sterile
Sterilization (microbiology)
Sterilization is a term referring to any process that eliminates or kills all forms of microbial life, including transmissible agents present on a surface, contained in a fluid, in medication, or in a compound such as biological culture media...
loop of wire, sometimes known as an inoculator, is streaked across the surface of the agar leaving organisms behind, a higher number at the beginning of the streak and a lower number at the end. At some point during a successful "streak", the number of organisms deposited will be such that distinct individual colonies will grow in that area which may be removed for further culturing, using another sterile loop.
History
In 1881, Fannie Hesse, who was working as a technician for her husband in the laboratory of Robert KochRobert Koch
Heinrich Hermann Robert Koch was a German physician. He became famous for isolating Bacillus anthracis , the Tuberculosis bacillus and the Vibrio cholerae and for his development of Koch's postulates....
, suggested agar as an effective setting agent since it had been common place in jam making for some time.
Types
Growth medium
A growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens.There are different types of media for growing different types of cells....
, the formulations of agar used in plates may be classified as either "defined" or "undefined"; defined medium is synthesized from individual chemicals required by the organism so that the exact molecular composition is known, whereas undefined medium is made from natural products such as yeast extract
Yeast extract
Yeast extract is the common name for various forms of processed yeast products made by extracting the cell contents ; they are used as food additives or flavourings, or as nutrients for bacterial culture media. They are often used to create savory flavors and umami taste sensations. Monosodium...
, where the precise composition is unknown.
Agar plates may be formulated as either permissive, with the intent of allowing the growth of whatever organisms are present, or restrictive or selective, with the intent of only allowing growth a particular subset of those organisms. This may take the form of a nutritional requirement, for instance providing a particular compound such as lactose
Lactose
Lactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose. Lactose makes up around 2~8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from or , the Latin word for milk,...
as the only source of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...
and thereby selecting only organisms which can metabolize
Metabolism
Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
that compound, or by including a particular antibiotic or other substance in order to select only organisms which are resistant
Antibiotic resistance
Antibiotic resistance is a type of drug resistance where a microorganism is able to survive exposure to an antibiotic. While a spontaneous or induced genetic mutation in bacteria may confer resistance to antimicrobial drugs, genes that confer resistance can be transferred between bacteria in a...
to that substance. This correlates to some degree with defined and undefined media; undefined media, made from natural products and containing an unknown combination of very many organic molecules, is typically more permissive in terms of supplying the needs of a wider variety of organisms, while defined media can be precisely tailored to select organisms with specific properties.
Agar plates may also be indicator plates, in which the organisms are not selected on the basis of growth, but are instead distinguished by a color change in some colonies, typically caused by the action of an enzyme
Enzyme
Enzymes are proteins that catalyze chemical reactions. In enzymatic reactions, the molecules at the beginning of the process, called substrates, are converted into different molecules, called products. Almost all chemical reactions in a biological cell need enzymes in order to occur at rates...
on some compound added to the media.
Some commonly used agar plate types are:
Blood agar types
Blood agar plate (BAP) Contains mammalian blood (usually sheep or horse), typically at a concentration of 5–10%. BAP are enriched, differential media used to isolate fastidious
Growth medium
A growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens.There are different types of media for growing different types of cells....
organisms and detect hemolytic
Hemolysis (microbiology)
Hemolysis is the breakdown of red blood cells. The ability of bacterial colonies to induce hemolysis when grown on blood agar is used to classify certain microorganisms. This is particularly useful in classifying streptococcal species...
activity. β-hemolytic activity will show lysis and complete digestion of red blood cell contents surrounding colony. Examples include Streptococcus haemolyticus. α-hemolysis will only partially lyse (the cells are either lysed or not- it is the digestion that may be incomplete) the hemoglobin and will appear green. An example of this would be Streptococcus viridans. γ-hemolysis (or non-hemolytic) is the term referring to a lack of hemolytic activity.
Contains meat extract, tryptone
Tryptone
Tryptone is the assortment of peptides formed by the digestion of casein by the protease trypsin.Tryptone is commonly used in microbiology to produce Lysogeny broth for the growth of E. coli and other microorganisms...
, sodium chloride
Sodium chloride
Sodium chloride, also known as salt, common salt, table salt or halite, is an inorganic compound with the formula NaCl. Sodium chloride is the salt most responsible for the salinity of the ocean and of the extracellular fluid of many multicellular organisms...
, and agar.
Chocolate agar
Chocolate agar
Chocolate agar
Chocolate agar - is a non-selective, enriched growth medium. It is a variant of the blood agar plate. It contains red blood cells, which have been lysed by heating very slowly to 56 °C. Chocolate agar is used for growing fastidious respiratory bacteria, such as Haemophilus influenzae...
(CHOC) is a type of blood agar plate in which the blood cells have been lysed
Lysis
Lysis refers to the breaking down of a cell, often by viral, enzymic, or osmotic mechanisms that compromise its integrity. A fluid containing the contents of lysed cells is called a "lysate"....
by heating the cells to 56 °C. Chocolate agar is used for growing fastidious (fussy) respiratory bacteria, such as Haemophilus influenzae
Haemophilus influenzae
Haemophilus influenzae, formerly called Pfeiffer's bacillus or Bacillus influenzae, Gram-negative, rod-shaped bacterium first described in 1892 by Richard Pfeiffer during an influenza pandemic. A member of the Pasteurellaceae family, it is generally aerobic, but can grow as a facultative anaerobe. H...
. No chocolate
Chocolate
Chocolate is a raw or processed food produced from the seed of the tropical Theobroma cacao tree. Cacao has been cultivated for at least three millennia in Mexico, Central and South America. Its earliest documented use is around 1100 BC...
is actually contained in the plate; it is named for the coloration only.
Horse blood agar
Horse blood agar (HBA
HBA
HBA can refer to:* Health and beauty aids, a term used for cosmetics and toiletry items* Honours Bachelor of Arts* Hobart International Airport * Hewa Bora Airways...
) is a type of blood enriched microbiological culture media. As it is enriched, it allows the growth of certain fastidious bacteria, and allows indication of haemolytic activity in these bacterial cultures.
Thayer-Martin agar
Thayer-Martin agar
Thayer-Martin agar
Thayer-Martin agar is a Mueller-Hinton agar with 5% chocolate sheep blood and antibiotics. It is used for culturing and primarily isolating pathogenic Neisseria bacteria, including Neisseria gonorrhoeae and Neisseria meningitidis, as the medium inhibits the growth of most other microorganisms...
(TM) is a chocolate agar designed to isolate Neisseria gonorrhoeae
Neisseria gonorrhoeae
Neisseria gonorrhoeae, also known as gonococci , or gonococcus , is a species of Gram-negative coffee bean-shaped diplococci bacteria responsible for the sexually transmitted infection gonorrhea.N...
.
Thiosulfate-citrate-bile salts-sucrose agar
Thiosulfate-citrate-bile salts-sucrose agar (TCBS) enhances growth of Vibrio spp.
Vibrio
Vibrio is a genus of Gram-negative bacteria possessing a curved rod shape, several species of which can cause foodborne infection, usually associated with eating undercooked seafood. Typically found in saltwater, Vibrio are facultative anaerobes that test positive for oxidase and do not form...
, including Vibrio cholerae
Vibrio cholerae
Vibrio cholerae is a Gram-negative, comma-shaped bacterium. Some strains of V. cholerae cause the disease cholera. V. cholerae is facultatively anaerobic and has a flagella at one cell pole. V...
General bacterial media
- Bile esculin agarBile esculin agarBile Esculin Agar is a selective differential agar used to isolate and identify members of the genus Enterococcus, also known as "group D streptococci".-Composition and process:...
(BEA)
- BEA is used for the isolation of EnterococciEnterococcusEnterococcus is a genus of lactic acid bacteria of the phylum Firmicutes. Enterococci are Gram-positive cocci that often occur in pairs or short chains, and are difficult to distinguish from streptococci on physical characteristics alone. Two species are common commensal organisms in the...
as well as Group D StreptococciStreptococcusStreptococcus is a genus of spherical Gram-positive bacteria belonging to the phylum Firmicutes and the lactic acid bacteria group. Cellular division occurs along a single axis in these bacteria, and thus they grow in chains or pairs, hence the name — from Greek στρεπτος streptos, meaning...
- CLED agarCLED agarCLED agar is a valuable non-inhibitory growth medium used in the isolation and differentiation of urinary organisms. Being electrolyte deficient, it prevents the swarming of Proteus species. Cystine promotes the formation of cystine-dependent dwarf colonies...
(CysteineCysteineCysteine is an α-amino acid with the chemical formula HO2CCHCH2SH. It is a non-essential amino acid, which means that it is biosynthesized in humans. Its codons are UGU and UGC. The side chain on cysteine is thiol, which is polar and thus cysteine is usually classified as a hydrophilic amino acid...
LactoseLactoseLactose is a disaccharide sugar that is found most notably in milk and is formed from galactose and glucose. Lactose makes up around 2~8% of milk , although the amount varies among species and individuals. It is extracted from sweet or sour whey. The name comes from or , the Latin word for milk,...
Electrolyte Deficient agar)
- CLED agar
- CLED agar is used to isolate and differentiate urinary tract bacteria, since it inhibits ProteusProteus (bacterium)Proteus is a genus of Gram-negative Proteobacteria.-Clinical significance:Three species—P. vulgaris, P. mirabilis, and P. penneri—are opportunistic human pathogens. Proteus includes pathogens responsible for many human urinary tract infections. P. mirabilis causes wound and urinary...
species swarming and can differentiate between lactose fermenters and non-fermenters.- Hektoen enteric agarHektoen enteric agarHektoen enteric agar is a selective and differential agar primarily used to recover Salmonella and Shigella from patient specimens. HE contains indicators of lactose fermentation and H2S production; as well as inhibitors to prevent the growth of gram positive bacteria...
(HEA)
- Hektoen enteric agar
- HE agar is designed to isolate and recover fecal bacteria belonging to the EnterobacteriaceaeEnterobacteriaceaeThe Enterobacteriaceae is a large family of bacteria that includes many of the more familiar pathogens, such as Salmonella, Escherichia coli, Yersinia pestis, Klebsiella and Shigella. This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria in the...
family. HE is particularly useful in isolating SalmonellaSalmonellaSalmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...
and ShigellaShigellaShigella is a genus of Gram-negative, nonspore forming, non-motile, rod-shaped bacteria closely related to Escherichia coli and Salmonella. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and apes. During...
.- Lysogeny BrothLysogeny brothLysogeny broth , a nutritionally rich medium, is primarily used for the growth of bacteria. The acronym has been incorrectly interpreted as Luria broth, Lennox broth, or Luria-Bertani medium; according to its creator Giuseppe Bertani, the abbreviation LB was actually intended to stand for lysogeny...
(LB) - MacConkey agarMacConkey agarMacConkey agar is a culture medium designed to grow Gram-negative bacteria and stain them for lactose fermentation.-Contents:It contains bile salts MacConkey agar is a culture medium designed to grow Gram-negative bacteria and stain them for lactose fermentation.-Contents:It contains bile salts...
(MAC)
- Lysogeny Broth
- A selective and differential media used to differentiate between Gram negative bacteria while inhibiting the growth of Gram positive bacteria. The addition of bile salts and crystal violetCrystal violetCrystal violet or Gentian violet is a triarylmethane dye. The dye is used as a histological stain and in Gram’s method of classifying bacteria. Crystal violet has antibacterial, antifungal, and anthelmintic properties and was formerly important as a topical antiseptic...
to the agar inhibits the growth of most Gram positive bacteria, making MacConkey agar selective. Lactose and neutral redNeutral redNeutral Red is a eurhodin dye used for staining in histology. It stains lysosomes red. It is used as a general stain in histology, as a counterstain in combination with other dyes, and for many staining methods. Together with Janus Green B, it is used to stain embryonal tissues and supravital...
are added to differentiate the lactose fermenters, which form pink colonies, from lactose nonfermenters that form clear colonies. An alternative media, eosin methylene blueEosin methylene blueEosin methylene blue is a slightly selective stain for Gram-negative bacteria. It is a blend of two stains, eosin and methylene blue in the ratio of 6:1...
(EMB) serves a similar purpose.- Mannitol salt agarMannitol Salt AgarMannitol salt agar or MSA is a commonly used growth medium in microbiology. It encourages the growth of a group of certain bacteria while inhibiting the growth of others. This medium is important in medical laboratories by distinguishing pathogenic microbes in a short period of time...
(MSA)
- Mannitol salt agar
- MSA is also a selective and differential media. The mannitolMannitolMannitol is a white, crystalline organic compound with the formula . This polyol is used as an osmotic diuretic agent and a weak renal vasodilator...
indicates organisms that ferment mannitol: mannitol fermentation produces lactic acidLactic acidLactic acid, also known as milk acid, is a chemical compound that plays a role in various biochemical processes and was first isolated in 1780 by the Swedish chemist Carl Wilhelm Scheele. Lactic acid is a carboxylic acid with the chemical formula C3H6O3...
, lowering the pH and turning the plate yellow. The salt is to select for halophileHalophileHalophiles are extremophile organisms that thrive in environments with very high concentrations of salt. The name comes from the Greek for "salt-loving". While the term is perhaps most often applied to some halophiles classified into the Archaea domain, there are also bacterial halophiles and some...
s; organisms that cannot withstand a high salt content will be unable to grow well.- Mueller-Hinton agarMueller-Hinton agarMüller-Hinton agar is an microbiological growth medium that is commonly used for antibiotic susceptibility testing. It is also used to isolate and maintain Neisseria and Moraxella species.It typically contains :*30.0% beef infusion...
(MHA)
- Mueller-Hinton agar
- MHA contains beef infusion, peptone, and starchStarchStarch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store...
and is used primarily for antibiotic susceptibility testing. It can be in a form of blood agar.
- Nutrient agarNutrient agarNutrient agar is a microbiological growth medium commonly used for the routine cultivation of non-fastidious bacteria. It is useful because it remains solid even at relatively high temperatures. Also, bacteria grown in nutrient agar grows on the surface, and is clearly visible as small colonies...
- Nutrient agar is usually used for growth of non-fastidious organisms and observation of pigment production. It is safe to use in school science laboratories because it does not selectively grow pathogenPathogenA pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
ic bacteria.- Önöz agar
- Önöz agar allows more rapid bacteriological diagnosis as SalmonellaSalmonellaSalmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...
and ShigellaShigellaShigella is a genus of Gram-negative, nonspore forming, non-motile, rod-shaped bacteria closely related to Escherichia coli and Salmonella. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and apes. During...
colonies can be clearly and reliably differentiated from other EnterobacteriaceaeEnterobacteriaceaeThe Enterobacteriaceae is a large family of bacteria that includes many of the more familiar pathogens, such as Salmonella, Escherichia coli, Yersinia pestis, Klebsiella and Shigella. This family is the only representative in the order Enterobacteriales of the class Gammaproteobacteria in the...
. The yields of Salmonella from stool samples obtained, when using this medium, are higher than those obtained with LEIFSON Agar or Salmonella–Shigella agar (SSA).- Phenylethyl alcohol agar (PEA)
- PEA selects for StaphylococcusStaphylococcusStaphylococcus is a genus of Gram-positive bacteria. Under the microscope they appear round , and form in grape-like clusters....
species while inhibiting Gram-negativeGram-negativeGram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
bacilli (e.g. Escherichia coliEscherichia coliEscherichia coli is a Gram-negative, rod-shaped bacterium that is commonly found in the lower intestine of warm-blooded organisms . Most E. coli strains are harmless, but some serotypes can cause serious food poisoning in humans, and are occasionally responsible for product recalls...
, ShigellaShigellaShigella is a genus of Gram-negative, nonspore forming, non-motile, rod-shaped bacteria closely related to Escherichia coli and Salmonella. The causative agent of human shigellosis, Shigella causes disease in primates, but not in other mammals. It is only naturally found in humans and apes. During...
, ProteusProteus (bacterium)Proteus is a genus of Gram-negative Proteobacteria.-Clinical significance:Three species—P. vulgaris, P. mirabilis, and P. penneri—are opportunistic human pathogens. Proteus includes pathogens responsible for many human urinary tract infections. P. mirabilis causes wound and urinary...
, etc.).- R2A AgarR2a agarR2A agar is a culture medium developed to study bacteria which normally inhabit potable water. These bacteria tend to be slow-growing species and would quickly be suppressed by faster-growing species on a richer culture medium....
(R2A)
- R2A Agar
- A non-specific agar that imitates the medium of water. Used for water analysis.
- Tryptic (Trypticase) Soy AgarTrypticase soy agarTrypticase soy agar is a bacterial growth medium.The medium contains enzymatic digests of casein and soybean meal which provides amino acids and other nitrogenous substances making it a nutritious medium for a variety of organisms. Glucose is the energy source. Sodium chloride maintains the osmotic...
(TSA)
- Tryptic (Trypticase) Soy Agar
- TSA is a general purpose media produced via enzymatic digestion of soybeanSoybeanThe soybean or soya bean is a species of legume native to East Asia, widely grown for its edible bean which has numerous uses...
meal and caseinCaseinCasein is the name for a family of related phosphoprotein proteins . These proteins are commonly found in mammalian milk, making up 80% of the proteins in cow milk and between 60% and 65% of the proteins in human milk....
. TSA is frequently the base media of other agar types; for example, blood agar plates are made by enriching TSA plates with blood (see above). - TSA plates support growth of many semi-fastidious bacteria, including some species of BrucellaBrucellaBrucella is a genus of Gram-negative bacteria. They are small , non-motile, non-encapsulated coccobacilli, which function as facultative intracellular parasites....
, CorynebacteriumCorynebacteriumCorynebacterium is a genus of Gram-positive rod-shaped bacteria. They are widely distributed in nature and are mostly innocuous. Some are useful in industrial settings such as C. glutamicum. Others can cause human disease. C...
, Listeria, NeisseriaNeisseriaThe Neisseria is a large genus of commensal bacteria that colonize the mucosal surfaces of many animals. Of the 11 species that colonize humans, only two are pathogens. N. meningitidis and N. gonorrhoeae often cause asymptomatic infections, a commensal-like behavior...
, and VibrioVibrioVibrio is a genus of Gram-negative bacteria possessing a curved rod shape, several species of which can cause foodborne infection, usually associated with eating undercooked seafood. Typically found in saltwater, Vibrio are facultative anaerobes that test positive for oxidase and do not form...
.- XyloseXLD agarXylose lysine deoxycholate agar is a selective growth medium used in the isolation of Salmonella and Shigella species from clinical samples and from food. It has a pH of approximately 7.4, leaving it with a bright pink or red appearance due to the indicator phenol red. Sugar fermentation lowers...
-LysineLysineLysine is an α-amino acid with the chemical formula HO2CCH4NH2. It is an essential amino acid, which means that the human body cannot synthesize it. Its codons are AAA and AAG....
-Deoxycholate agar (XLD)
- Xylose
- XLD is used for the culture of stoolHuman fecesHuman feces , also known as a stool, is the waste product of the human digestive system including bacteria. It varies significantly in appearance, according to the state of the digestive system, diet and general health....
samples and contains two indicators. It is formulated to inhibit Gram-positive bacteria, while the growth of Gram-negative bacilliBacilliBacilli refers to a taxonomic class of bacteria. It includes two orders, Bacillales and Lactobacillales, which contain several well-known pathogens like Bacillus anthracis .-Ambiguity:...
is encouraged. The colonies of lactose fermenters appear yellow. - It is also used to culture possible SalmonellaSalmonellaSalmonella is a genus of rod-shaped, Gram-negative, non-spore-forming, predominantly motile enterobacteria with diameters around 0.7 to 1.5 µm, lengths from 2 to 5 µm, and flagella which grade in all directions . They are chemoorganotrophs, obtaining their energy from oxidation and reduction...
that may be present in a food sample. Most Salmonella colonies will produce a black centre on XLD.- Cetrimide agarCetrimide agarCetrimide agar is a type of agar used for the selective isolation of the gram-negative bacteria, Pseudomonas aeruginosa. As the name suggests, it contains cetrimide, which is the selective agent against alternate microbial flora...
- Cetrimide agar
- Cetrimide agar is a type of agar used for the selective isolation of the gram-negative bacteria, Pseudomonas aeruginosaPseudomonas aeruginosaPseudomonas aeruginosa is a common bacterium that can cause disease in animals, including humans. It is found in soil, water, skin flora, and most man-made environments throughout the world. It thrives not only in normal atmospheres, but also in hypoxic atmospheres, and has, thus, colonized many...
.- Tinsdale agar contains potassium tellurite, which can isolate Corynebacterium diphteriae.
Fungal media
- SabouraudRaymond SabouraudRaymond Sabouraud was a French physician born in Nantes. He specialized in dermatology and mycology, and was also an accomplished painter and sculptor....
agar
- Sabouraud agar is used to culture fungi and has a low pHPHIn chemistry, pH is a measure of the acidity or basicity of an aqueous solution. Pure water is said to be neutral, with a pH close to 7.0 at . Solutions with a pH less than 7 are said to be acidic and solutions with a pH greater than 7 are basic or alkaline...
that inhibits the growth of most bacteria; it also contains the antibiotic gentamicinGentamicinGentamicin is an aminoglycoside antibiotic, used to treat many types of bacterial infections, particularly those caused by Gram-negative organisms. However, gentamicin is not used for Neisseria gonorrhoeae, Neisseria meningitidis or Legionella pneumophila...
to specifically inhibit the growth of Gram-negativeGram-negativeGram-negative bacteria are bacteria that do not retain crystal violet dye in the Gram staining protocol. In a Gram stain test, a counterstain is added after the crystal violet, coloring all Gram-negative bacteria with a red or pink color...
bacteria.- Hay infusion agar
- Specific for the culturing of slime mouldSlime mouldSlime mold or mould is a broad term describing protists that use spores to reproduce. Slime molds were formerly classified as fungi, but are no longer considered part of this kingdom....
s (which are not fungi).- Potato dextrose agarPotato dextrose agarPotato dextrose agar and potato dextrose broth are common microbiological growth media made from potato infusion, and dextrose...
- Potato dextrose agar
- PDA is used to culture certain types of fungi.
- Malt extract agar
- Malt extract agar has a high content of peptone and is acidic. It is essentially used in the isolation of fungal microorganisms.
Moss media
- Knop agar
- Knop agar is used to culture axenically protonemaProtonemaA protonema is a thread-like chain of cells that forms the earliest stage of a bryophyte life cycle...
and whole mossMossMosses are small, soft plants that are typically 1–10 cm tall, though some species are much larger. They commonly grow close together in clumps or mats in damp or shady locations. They do not have flowers or seeds, and their simple leaves cover the thin wiry stems...
plants, e.g. those of Physcomitrella patensPhyscomitrella patensPhyscomitrella patens is a moss used as a model organism for studies on plant evolution, development and physiology.-Model organism:...
, a model organismModel organismA model organism is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the organism model will provide insight into the workings of other organisms. Model organisms are in vivo models and are widely used to...
.
See also
- Growth mediumGrowth mediumA growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella patens.There are different types of media for growing different types of cells....
- MRS agarMRS agarOften abbreviated to MRS, this type of bacterial growth medium is so-named by its inventors: de Man, Rogosa and Sharpe. Developed in 1960, this medium was designed to favour the luxuriant growth of Lactobacilli for lab study...
- Petri dishPetri dishA Petri dish is a shallow glass or plastic cylindrical lidded dish that biologists use to culture cells or small moss plants. It was named after German bacteriologist Julius Richard Petri, who invented it when working as an assistant to Robert Koch...
- R2a agarR2a agarR2A agar is a culture medium developed to study bacteria which normally inhabit potable water. These bacteria tend to be slow-growing species and would quickly be suppressed by faster-growing species on a richer culture medium....
- Replica platingReplica platingIn molecular biology and microbiology, replica plating is a technique in which one or more secondary Petri plates containing different solid selective growth media are inoculated with the same colonies of microorganisms from a primary plate , reproducing the original spatial...
- Viral plaqueViral plaqueA viral plaque is a visible structure formed within a cell culture, such as bacterial cultures within some nutrient medium . The bacteriophage viruses replicate and spread, thus generating regions of cell destructions known as plaques....