Microbiological culture
A microbiological culture, or microbial culture, is a method of multiplying
The term culture can also refer to the microorganisms being grown.
Microbial cultures are used to determine the type of organism, its abundance in the sample being tested, or both. It is one of the primary
It is often essential to isolate a pure culture of microorganisms. A pure (or axenic) culture is a population of
History
The first culture media was liquid media, designed by Louis Pasteur in 1860.[2] This was used in the laboratory until Robert Koch's development of solid media in 1881.[3] Koch's method of using a flat plate for his solid media was replaced by Julius Richard Petri's round box in 1887.[2] Since these foundational inventions, a diverse array of media and methods have evolved to help scientists grow, identify, and purify cultures of microorganisms.
Types of microbial cultures
Prokaryotic culture
The culturing of prokaryotes typically involves bacteria, since archaea are difficult to culture in a laboratory setting.[4] To obtain a pure prokaryotic culture, one must start the culture from a single cell or a single colony of the organism.[5] Since a prokaryotic colony is the asexual offspring of a single cell, all of the cells are genetically identical and will result in a pure culture.
Viral culture
Eukaryotic cell culture
Eukaryotic cell cultures provide a controlled environment for studying eukaryotic organisms. Single-celled eukaryotes - such as yeast, algae, and protozoans - can be cultured in similar ways to prokaryotic cultures. The same is true for multicellular microscopic eukaryotes, such as C. elegans.
Although macroscopic eukaryotic organisms are too large to culture in a laboratory, cells taken from these organisms can be cultured. This allows researchers to study specific parts and processes of a macroscopic eukaryote in vitro.
Culture methods
Method | Description | Uses and advantages |
---|---|---|
Liquid/broth cultures | Organisms are inoculated into a flask of liquid media | Growing up large volumes of organism, antimicrobial assays, bacterial differentiation |
Agar plates | Organisms are placed or streaked onto petri dishes | Provides a solid surface for stationary growth, compact and stackable |
Agar based dipsticks | Essentially miniature agar plates in the form of dipsticks | Diagnostic purposes, can be used anywhere, cost effective, easy to use |
Selective and differential media | Organisms are cultured in/on specific media to select for or differentiate between certain ones | Help identify unknown organisms, assist in purifying cultures |
Stab cultures | Organisms are inoculated into a test tube of solid agar | Short-term storage, bacterial differentiation |
Liquid cultures
One method of microbiological culture is liquid culture, in which the desired organisms are suspended in a liquid nutrient medium, such as
Liquid cultures are ideal for preparation of an antimicrobial assay in which the liquid broth is inoculated with bacteria and let to grow overnight (a ‘shaker’ may be used to mechanically mix the broth, to encourage uniform growth). Subsequently, aliquots of the sample are taken to test for the antimicrobial activity of a specific drug or protein (antimicrobial peptides).
Static liquid cultures may be used as an alternative. These cultures are not shaken, and they provide the microbes with an oxygen gradient.[6]
Agar plates
Microbiological cultures can be grown in petri dishes of differing sizes that have a thin layer of agar-based growth medium. Once the growth medium in the petri dish is inoculated with the desired bacteria, the plates are incubated at the optimal temperature for the growing of the selected bacteria (for example, usually at 37 degrees Celsius, or the human body temperature, for cultures from humans or animals, or lower for environmental cultures). After the desired level of growth is achieved, agar plates can be stored upside down in a refrigerator for an extended period of time to keep bacteria for future experiments.
There are a variety of additives that can be added to agar before it is poured into a plate and allowed to solidify. Some types of bacteria can only grow in the presence of certain additives. This can also be used when creating engineered strains of bacteria that contain an antibiotic-resistance gene. When the selected antibiotic is added to the agar, only bacterial cells containing the gene insert conferring resistance will be able to grow. This allows the researcher to select only the colonies that were successfully transformed.
Agar based dipsticks
Miniaturized version of agar plates implemented to dipstick formats, e.g. Dip Slide, Digital Dipstick
Selective and differential media
Selective and differential media reveal characteristics about the microorganisms being cultured on them. This kind of media can be selective, differential, or both selective and differential. Growing a culture on multiple kinds of selective and differential media can purify mixed cultures and reveal to scientists the characteristics needed to identify unknown cultures.
Selective media
Selective media is used to distinguish organisms by allowing for a specific kind of organism to grow on it while inhibiting the growth of others. For example, eosin methylene blue (EMB) may be used to select against Gram-positive bacteria, most of which have hindered growth on EMB, and select for Gram-negative bacteria, whose growth is not inhibited on EMB.[8]
Differential media
Scientists use differential media when culturing microorganisms to reveal certain biochemical characteristics about the organisms. These revealed traits can then be compared to attributes of known microorganisms in an effort to identify unknown cultures. An example of this is MacConkey agar (MAC), which reveals lactose-fermenting bacteria through a pH indicator that changes color when acids are produced from fermentation.[9]
Multitarget panels
On multitarget panels, bacteria isolated from a previously grown colony are distributed into each well, each of which contains growth medium as well as the ingredients for a biochemical test, which will change the absorbance of the well depending on the bacterial property for the tested target. The panel will be incubated in a machine, which subsequently analyses each well with a light-based method such as colorimetry, turbidimetry, or fluorometry.
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Multitarget microbial panel. A small amount of the bacteria to be tested is placed in each well, each of which has the ingredients for a separate test.
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Microbial panels loaded into an instrument used for automated antibiotic sensitivity testing of each well.
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A laboratory worker reviews results displayed on the screen of the automated analyzer.
Stab cultures
Stab cultures are similar to agar plates, but are formed by solid agar in a test tube. Bacteria is introduced via an inoculation needle or a pipette tip being stabbed into the center of the agar. Bacteria grow in the punctured area.[11] Stab cultures are most commonly used for short-term storage or shipment of cultures. Additionally, stab cultures can reveal characteristics about cultured microorganisms such as motility or oxygen requirements.
Solid plate culture of thermophilic microorganisms
For solid plate cultures of thermophilic microorganisms such as Bacillus acidocaldarius, Bacillus stearothermophilus, Thermus aquaticus and Thermus thermophilus etc. growing at temperatures of 50 to 70 degrees C, low acyl clarified gellan gum has been proven to be the preferred gelling agent comparing to agar for the counting or isolation or both of the above thermophilic bacteria.[12]
Cell Culture Collections
Microbial culture collections focus on the acquisition, authentication, production, preservation, cataloguing and distribution of viable cultures of standard reference microorganisms, cell lines and other materials for research in microbial systematics.[13][14] Culture collection are also repositories of type strains.
Collection Acronym | Name | Location |
---|---|---|
ATCC | American Type Culture Collection
|
Manassas, Virginia
|
BCCM | Belgian Co-ordinated Collections of Micro-organisms | Decentralized, Coordination Cell in Brussels, Belgium |
CCUG | Culture Collection University of Gothenburg | Gothenburg, Sweden |
CECT | Colección Española de Cultivos Tipo | Valencia, Spain |
CIP | Collection d'Institut Pasteur | Paris, France |
DSMZ | Deutsche Sammlung von Mikroorganismen und Zellkulturen
|
Braunschweig, Germany |
NCPPB | National Collection of Plant Pathogenic Bacteria | York, UK |
ICMP | International Collection of Microorganisms from Plants | Auckland, New Zealand |
JCM | Japan Collection of Microorganisms | Tsukuba, Ibaraki, Japan
|
NCTC | National Collection of Type Cultures | Public Health England, London, United Kingdom |
NCIMB | National Collection of Industrial, Food and Marine Bacteria | Aberdeen, Scotland |
NCPPB | National Collection of Plant Pathogenic Bacteria | York, England |
See also
- Colony-forming unit
- Blood culture
- Microbial dark matter
- Microbial Food Cultures
- Screening cultures
- Sputum culture
- Synchronous culture
- Gellan gum
References
- ^ Healthwise, Incorporated (2010-06-28). "Throat Culture". WebMD. Archived from the original on 2013-03-17. Retrieved 2013-03-10.
- ^ PMID 31956419.
- PMID 26124557.
- PMID 38132325.
- – via Oxford Academic.
- PMID 4914569.
- PMID 33169747.
- ^ "6.3C: Selective and Differential Media". Biology LibreTexts. 2017-05-11. Retrieved 2024-03-03.
- PMID 32491326, retrieved 2024-03-03
- ISBN 978-0-323-41315-2.
- ^ "Addgene: Streaking a Plate from an Addgene Stab Culture". www.addgene.org. Archived from the original on 8 April 2018. Retrieved 21 March 2018.
- ^ Lin, Chi Chung and Casida, L. E. (1984) GELRITE as a Gelling Agent in Media for the Growth of Thermophilic Microorganisms. Applied and Environmental Microbiology 47, 427-429.
- ^ ISBN 9780321649638.
- ^ S2CID 19711069.
External links
- EFFCA - European Food and Feed Cultutes Association. Information about production and uses of microbial cultures as well as legislative aspects.