# Axenic

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{{Short description|Microbiological culture with only a single species or strain of organism}}
In [biology](/source/biology), '''axenic''' ({{IPAc-en|eɪ|ˈ|z|ɛ|n|ɪ|k}}, {{IPAc-en|eɪ|ˈ|z|i|n|ɪ|k}}) describes the state of a [culture](/source/Microbiological_culture) in which only a single species, variety, or strain of [organism](/source/organism) is present and entirely free of all other [contaminating](/source/contaminating) organisms. The earliest axenic cultures were  of  [bacteria](/source/bacteria) or unicellular [eukaryote](/source/eukaryote)s, but axenic cultures of many multicellular organisms are also possible.<ref>{{Cite book
  | last1 = Thain| first1 = M.
  | last2 = Hickman | first2 = M.
  | title = Dictionary of Biology
  | publisher = [Penguin Books](/source/Penguin_Books), London, UK
  | year = 1994
  | isbn = 0-14-051288-8
  | edition = 9th
 }}</ref> Axenic culture is an important tool for the study of [symbiotic](/source/symbiotic) and [parasitic](/source/parasitic) organisms in a controlled environment.

==Preparation==
Axenic cultures of [microorganism](/source/microorganism)s are typically prepared by [subculture](/source/Subculture_(biology)) of an existing mixed culture. This may involve use of a [dilution series](/source/serial_dilution), in which a culture is successively diluted to the point where subsamples of it contain only a few individual organisms, ideally only a single individual (in the case of an [asexual](/source/asexual_reproduction) [species](/source/species)). These subcultures are allowed to grow until the identity of their constituent organisms can be ascertained. Selection of those cultures consisting solely of the desired organism produces the axenic culture. Subculture selection may also involve manually sampling the target organism from an uncontaminated growth front in an otherwise mixed culture, and using this as an inoculum source for the subculture.<ref>{{cite journal|title=Preparation of Axenic Cultures of Algae by Use of a French Press |author1=J.B. Middlebrook |author2=R.O. Bowman |date=9 September 1963 |journal= Applied Microbiology|volume=12 |issue=1 |pmc=1058062 |pmid=14106939 |pages=44–5|doi=10.1128/am.12.1.44-45.1964 }}</ref>

Axenic cultures are usually checked routinely to ensure that they remain axenic.  One standard approach with microorganisms is to spread a sample of the culture onto an [agar plate](/source/agar_plate), and to [incubate](/source/Incubator_(microbiology)) this for a fixed period of time.  The agar should be an enriched medium that will support the growth of common "contaminating" organisms.  Such "contaminating" organisms will grow on the plate during this period, identifying cultures that are no longer axenic.{{citation needed|date=February 2020}}

==Experimental use==
As axenic cultures are derived from very few organisms, or even a single individual, they are useful because the organisms present within them share a relatively narrow [gene pool](/source/gene_pool). In the case of an asexual species derived from a single individual, the resulting culture should consist of  [identical](/source/Cloning) organisms (though processes such as [mutation](/source/mutation) and [horizontal gene transfer](/source/horizontal_gene_transfer) may introduce a degree of variability).  Consequently, they will generally respond in a more uniform and [reproducible](/source/Reproducibility) fashion, simplifying the interpretation of [experiment](/source/experiment)s.

===Problems===
The axenic culture of some pathogens is complicated because they normally thrive within host tissues which exhibit properties that are difficult to replicate ''in vitro''.  This is especially true in the case of [intracellular pathogens](/source/intracellular_parasite).  However, careful replication of key features of the host environment can resolve these difficulties (e.g. host [metabolite](/source/metabolite)s, [dissolved oxygen](/source/oxygen_saturation)), such as with the [Q fever](/source/Q_fever) pathogen, ''[Coxiella burnetii](/source/Coxiella_burnetii)''.<ref>{{cite journal | last=Omsland | first=Anders | year=2009 | title=Host cell-free growth of the Q fever bacterium ''Coxiella burnetii'' | journal=[PNAS](/source/PNAS) | volume=106 | pages=4430–4434 | doi=10.1073/pnas.0812074106 | pmid=19246385 | issue=11 | pmc=2657411 |display-authors=etal| bibcode=2009PNAS..106.4430O | doi-access=free }}</ref>

==See also==
* [Asepsis](/source/Asepsis)
* [Gnotobiotic animal](/source/Gnotobiotic_animal)
** [Germ-free animal](/source/Germ-free_animal)
* [Sterilization (microbiology)](/source/Sterilization_(microbiology))

==References==
{{reflist|2}}

{{Bacteria}}
Category:Bacteria
Category:Bacteriology
Category:Biotechnology
Category:Cell biology
Category:Cell culture
Category:Microbiology techniques
Category:Microbiology terms

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