Agar plate 254713 215782356 2008-05-29T18:09:10Z 189.181.162.45 /* General bacterial media */ {{Infobox Laboratory equipment |name = Agar plate |image = Agar plate with colonies.jpg |caption = An agar plate streaked with microorganisms isolated from a [[Deep sea|deep-water]] [[Sea sponge|sponge]]. Individual colonies may be seen center right. |acronym = |other_names = |uses = [[Microbiological culture|Culturing]] |inventor = |manufacturer = |model = |related = [[Petri dish]]<br/>[[Growth medium]] }} An '''agar plate''' is a sterile [[Petri dish]] that contains a [[growth medium]] (typically [[agar]] plus nutrients) used to [[Microbiological culture|culture]] [[microorganisms]]. [[Growth medium|Selective]] growth compounds may also be added to the media, such as [[antibiotic]]s.<ref name=Brock>{{cite book | author = Madigan M, Martinko J (editors). | title = Brock Biology of Microorganisms | edition = 11th ed. | publisher = Prentice Hall | year = 2005 | isbn =0131443291 }}</ref> Individual microorganisms placed on the plate will grow into individual [[colony (biology)|colonies]], each a [[cloning|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 [[Microbiological culture|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, [[sterilization (microbiology)|sterile]] loop of wire is "[[Streaking (microbiology)|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.<ref name=Brock /> For information on agar plate preparation, please visit the [[wikibooks:School_science/Agar plate|Wikibooks Agar Plate page]]. == Types of agar plates == [[Image:Quintote_colony_counter.jpg|thumb|left|An agar plate being viewed in an electronic [[colony counter]].]] Like other [[growth medium|growth media]], the formulations of agar used in plates may be classified as either '''defined''' or '''undefined'''; defined medium being synthesized from the individual chemicals as required by the organism so that the exact molecular composition is known, while undefined medium is made up of natural products such as [[yeast extract]], where the precise composition is unknown.<ref name=Baron>{{cite book | author = Baron S ''et al'', (editors). | title = Baron's Medical Microbiology | edition = 4th ed. | publisher = Univ of Texas Medical Branch | year = 1996 | id = [http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Search&db=books&doptcmdl=GenBookHL&term=Culture+AND+mmed%5Bbook%5D+AND+147423%5Buid%5D&rid=mmed.section.5451#5457 (via NCBI Bookshelf)] ISBN 0-9631172-1-1 }}</ref> 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 selecting for growth a particular subset of those organisms.<ref name=Sherris>{{cite book | author = Ryan KJ; Ray CG (editors) | title = Sherr KEEP DREAMINGis Medical Microbiology | edition = 4th ed. | publisher = McGraw Hill | year = 2004 | id = ISBN 0838585299 }}</ref> This may take the form of a nutritional requirement, for instance providing a particular compound such as [[lactose]] as the only source of [[carbon]] for [[energy]] and material and thereby selecting only organisms which can [[metabolism|metabolize]] that compound, or by including a particular antibiotic or other substance in order to select only organisms which are [[antibiotic resistance|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 very specific properties. Agar plates may also be '''indicator''' plates, where the organisms are not selected on the basis of growth, but a compound in the agar is altered by an [[enzyme]] or similar in some colonies so as to change color and identify them from those lacking the enzyme. Some commonly used agar plate types are: [[Image:Agarplate redbloodcells edit.jpg|250px|thumb|right|Blood agar plates are often used to diagnose infection. On the left is a positive ''[[Staphylococcus]]'' infection; on the right a positive ''[[Streptococcus]]'' culture.]] === Blood agar types === * Blood agar plate (BAP) : Contains mammalian blood (usually sheep or horse), typically at a concentration of 5&ndash;10%. BAP are an enriched, differential media used to isolate [[Growth medium|fastidious]] organisms and detect [[Hemolysis (microbiology)|hemolytic]] activity. β-hemolytic activity will show complete lysis of red blood cells surrounding colony. Examples include ''Streptococcus haemolyticus''. α-hemolysis will only partially lyse 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. * Chocolate agar (CHOC) : A type of blood agar plate in which the blood cells have been [[Lysis|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.) * [[Thayer-Martin agar]] (TM) : Chocolate agar designed to isolate ''[[Neisseria gonorrhoeae]]''. === General bacterial media === [[Image:Agarplates.jpg|right|thumb|Four types of agar plates demonstrating differential growth depending on bacterial metabolism.]] * [[Bile esculin agar]] (BEA) : BEA is used for the isolation of [[Enterococcus|Enterococci]] as well as [[Streptococcus|Group D Streptococci]] * [[CLED agar|Cysteine Lactose Electrolyte Deficient agar]] (CLED) : CLED agar is used to isolate and differentiate urinary tract bacteria, since it inhibits ''[[Proteus (bacterium)|Proteus]]'' species swarming and can differentiate between lactose fermenters and non-fermenters. * [[Hektoen enteric agar]] (HEA) : HE agar is designed to isolate and recover fecal bacteria belonging to the [[Enterobacteriaceae]] family. HE is particularly useful in isolating ''[[Salmonella]]'' and ''[[Shigella]]''. * [[Lysogeny Broth|Luria Broth]] (LB) * [[MacConkey agar]] (MAC) : 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 violet]] to the agar inhibits the growth of most Gram positive bacteria, making MacConkey agar selective. Lactose and neutral red are added to differentiate the lactose fermenters, which form pink colonies, from lactose nonfermenters that form clear colonies. An alternative media, [[eosin methylene blue]] (EMB) serves a similar purpose. * [[Mannitol salt agar]] (MSA) : MSA is also a selective and differential media. [[Mannitol]] is the differential part, it indicates organisms that ferment mannitol. If mannitol fermentation is occurring, lactic acid will be produced, and the pH will drop causing the MSA plate to turn yellow. The salt portion is selective for [[halophile]]s; organisms that cannot withstand a high salt content will be unable to grow well. * [[Mueller-Hinton agar]] (MHA) : MHA contains beef infusion, peptone, and starch used primarily for antibiotic susceptibility testing. It can be in a form of blood agar. [[Image:Ascomycetes.jpg|thumb|right|Fungi growing in axenic culture ([[ascomycetes]])]] * [[Nutrient agar]] : 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 [[pathogen]]ic bacteria. * [[Önöz agar]] : Önöz agar allows more rapid bacteriological diagnosis as ''[[Salmonella]]'' and ''[[Shigella]]'' colonies can be clearly and reliably differentiated from other [[Enterobacteriaceae]]. The yields of ''Salmonella'' from stool samples obtained, when using this medium, are higher than those obtained with LEIFSON Agar or Salmonella&ndash;Shigella agar (SSA). * [[Phenylethyl alcohol agar]] (PEA) : PEA selects for ''[[Staphylococcus]]'' species while inhibiting [[Gram-negative]] bacilli (e.g. ''[[Escherichia coli]]'', ''[[Shigella]]'', ''[[Proteus (bacterium)|Proteus]]'', etc.). MSA is selective for ''Staphylococcus'' PEA is selective for gram positive bacteria [[Image:Aniger pda.jpg||thumb|right|''[[Aspergillus niger]]'' growing in potato dextrose agar]] * [[R2A Agar]] (R2A) : A non-specific agar that imitates the medium of water. Used for water analysis. * [[Trypticase soy agar|Tryptic (Trypticase) Soy Agar]] (TSA) : TSA is a general purpose media produced via enzymatic digestion of [[soybean]] meal and [[casein]]; TSA is frequently the base media of other agar plate type, i.e. blood agar plates (BAP) are made by enriching TSA plates with blood (see above). : TSA plates support growth of many semi-fastidious bacteria, including some species of ''[[Brucella]]'', ''[[Corynebacterium]]'', ''[[Listeria]]'', ''[[Neisseria]]'', and ''[[Vibrio]]''. * [[XLD agar|Xylose-Lysine-Deoxycholate agar]] (XLD) : XLD is used for the culture of [[stool]] samples, and contains two indicators. It is formulated to inhibit Gram-positive bacteria, while the growth of Gram-negative [[bacilli]] is encouraged. The colonies of lactose fermenters appear yellow. :It is also used to culture possible ''[[Salmonella]]'' that may be present in a food sample. ''Salmonella'' colonies will show a black halo on XLD. * [[Cetrimide agar]] :Cetrimide agar is a type of agar used for the selective isolation of the gram-negative bacteria, ''[[Pseudomonas aeruginosa]]''. === Fungal media === * [[Raymond Sabouraud|Sabouraud]] agar : Sabouraud agar is used to culture [[fungi]] and has a low [[pH]] that inhibits the growth of most bacteria; also contains the antibiotic [[gentamicin]] to specifically inhibit the growth of [[Gram-negative]] bacteria. * Hay Infusion agar : Specific for the culturing of [[slime moulds]] (though not technically fungi). * Potato dextrose agar : [[Potato dextrose broth|PDA]] is used to culture of certain types of [[fungi]]. == References == {{Reflist}} == See also == {{Commons|Agar plate}} * [[Growth medium]] * [[Petri dish]] * [[Replica plating]] * [[Viral plaque]] * [[R2a agar]] * [[MRS agar]] == External links == * [http://www.tgw1916.net/movies.html Video of sheep blood agar preparation] * [http://www.sciencebuddies.org/mentoring/project_ideas/MicroBio_Agar.shtml Science Buddies - All About Agar] {{Laboratory equipment}} [[Category:Microbiological media]] [[Category:Laboratory equipment]] [[Category:Microbiology terms]] [[Category:Microbiology equipment]] [[ja:寒天培地]] [[pl:Płytka agarowa]] [[simple:Agar plate]] [[zh:瓊脂平板]]