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. Furthermore, the term culture is more
generally used informally to refer to "selectively growing" a
specific kind of microorganism in the lab.
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
cell 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.
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 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
- http://www.webmd.com/a-to-z-guides/throat-culture
See also
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