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 both. It is one of the primary diagnostic methods of microbiology and used as a tool to determine the cause of infectious disease by letting the agent multiply in a predetermined media. For example, a throat culture is taken by scraping the lining of tissue in the back of the throat and blotting the sample into a media to be able to screen for harmful microorganisms, such as, streptococcus pyogenes, the caustive agent of strep throat. [1] Furthermore, the term culture is more generally used informally to refer to "selectively growing" a specific kind of microorganism in the lab.
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Microbial cultures are foundational and basic diagnostic methods used extensively as a research tool in molecular biology. It is often essential to isolate a pure culture of microorganisms. A pure (or axenic) culture is a population of cells or multicellular organisms growing in the absence of other species or types. A pure culture may originate from a single cell or single organism, in which case the cells are genetic clones of one another.
For the purpose of gelling the microbial culture, the medium of agarose gel (Agar) is used. Agar is a gelatinous substance derived from seaweed. A cheap substitute for agar is Guar gum, which can be used for the isolation and maintenance of thermophiles.
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Bacterial culture
Microbiological cultures utilize petri dishes of differing sizes that have a thin layer of agar based growth medium in them. Once the growth medium in the petri dish is inoculated with the desired bacteria, the plates are incubated in an oven usually set at 37 degrees Celsius. Another method of bacterial culture is liquid culture, in which case desired bacteria are suspended in liquid broth, a nutrient medium. These are ideal for preparation of an antimicrobial assay. The experimenter would inoculate liquid broth with a bacteria and let it grow overnight in a shaker for uniform growth, then take aliquots of the sample to test for the antimicrobial activity of a specific drug or protein (antimicrobial peptides).
Virus and phage culture
Virus or phage cultures require host cells for the virus or phage to multiply in. For bacteriophages, cultures are grown by infecting bacterial cells. The phage can then be isolated from the resulting plaques in a lawn of bacteria on a plate. Virus cultures are obtained from their appropriate eukaryotic host cells.
Eukaryotic cell culture
The term culture can also apply to eukaryotic microorganisms such as yeast and be used as a synonym for tissue culture, which involves the growth of cells or tissues explanted from a multi-cellular organism.
Isolation of pure cultures
For single-celled eukaryotes, such as yeast, the isolation of pure cultures uses the same techniques as for bacterial cultures. Pure cultures of multicellular organisms are often more easily isolated by simply picking out a single individual to initiate a culture. This is a useful technique for pure culture of fungi, multicellular algae, and small metazoa, for example.
Developing pure culture techniques is crucial to the observation of the specimen in question. The most common method to isolate individual cells and produce a pure culture, is to prepare a streak plate. The streak plate method is a way to physically separate the microbial population, and is done by spreading the inoculate back and forth with an inoculating loop over the solid agar plate. Upon incubation, colonies will arise and, hopefully, single cells will have been isolated from the biomass.
References
See also
- Blood culture
- Sputum culture
- Screening cultures
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