Microbiological culture
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A microbiological culture, AKA 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. Microbial cultures are also 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.
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[edit] Bacterial culture
The most common evolution of microbiological culture uses petri dishes with a layer of agar-based growth medium in them to grow bacterial cultures. This is generally done inside of an incubator. Another method is liquid culture, where the bacteria are grown suspended in a liquid nutrient medium. Bottles of liquid culture are often placed in shakers in order to introduce oxygen to the liquid and maintaining the uniformity of the culture.
[edit] Isolation of pure cultures
Pure cultures of single-celled organisms usually must be isolated and grown under aseptic conditions, requiring sterilized instruments and filtered or still air. Isolated colonies of microorganisms are usually obtained by growth on the surface of a petri dish. The petri dish (or plate) contains an appropriate growth medium for the microorganism of interest, usually gelled with agar. To isolate a pure culture, the initial sample (inoculum) is manipulated using with an inoculation loop or needle to spread and dilute the cells on the surface of the plate. The objective is to eventually have some areas of the petri dish with isolated single cells. The culture is incubated under appropriate environmental conditions until the cells have grown and visible colonies appear. Well-isolated colonies have a high probability of having grown from single cells and therefore being pure cultures.
Pure cultures can also be prepared by high dilution from a liquid culture into a liquid medium. At sufficient dilution only a fraction of the inoculated culture tubes grow, and the probability is high that those cultures originated from a single cell.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] See also
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