Introduction
Microorganisms need nutrients, a
source of energy and certain environmental conditions in order to grow and
reproduce. In the environment, microbes have adapted to the habitats most
suitable for their needs, in the laboratory, however, these requirements must
be met by a culture medium. This is basically an aqueous solution to which all
the necessary nutrients have been added. Depending on the type and combination
of nutrients, different categories of media can be made.
Complex media are rich in nutrients,
they contain water soluble extracts of plant or animal tissue (e.g.,
enzymatically digested animal proteins such as peptone and tryptone). Usually a
sugar, often glucose is added to serve as the main carbon and energy source.
The combination of extracts and sugar creates a medium which is rich in
minerals and organic nutrients, but since the exact composition is unknown, the
medium is called complex.
Defined media are media composed of
pure ingredients in carefully measured concentrations dissolved in double
distilled water i.e., the exact chemical composition of the medium is known.
Typically, they contain a simple sugar as the carbon and energy source, an
inorganic nitrogen source, various mineral salts and if necessary growth
factors (purified amino acids, vitamins, purines and pyrimidines).
Selective/differential media are media
based on either of the two categories above supplemented with growth-promoting
or growth-inhibiting additives. The additives may be species- or
organism-selective (e.g., a specific substrate, or an inhibitor such as
cyclohexamide (artidione) which inhibits all eucaryotic growth and is typically
used to prevent fungal growth in mixed cultures).
The mixture of necessary nutrients can
be used as a liquid medium, or a solidifying agent can be added. "Agar
agar" is a natural polysaccharide produced by marine algae and is the most
commonly used solidifying agent added to media (end concentration usually 1.5 %
w/v). If hydrolysis of the agar is suspected, a silica gel is used as a
replacement solidifying agent. The broth contains:
0.6 g/L "Lab-lemco" powder (a beef extract)
0.4 g/L yeast extract
1.0 g/L peptone (a nitrogen source)
1.0 g/L sodium chloride
3.0 g/L agar powder
An autoclave is an instrument used to sterilize equipment and
supplies by subjecting them to high pressure saturated steam at 121 °C for
around 15–20 minutes depending on the size of the load and the contents. It was
invented by Charles Chamberland in 1879, although a precursor known as the
steam digester was created by Denis Papin in 1679. The name comes from Greek
auto-, ultimately meaning self, and Latin clavis meaning key — a self-locking
device.
A autoclave is a device that
uses steam to sterilize equipment and other objects. This means that all
bacteria, viruses, fungi, and spores are inactivated. However, prions, like
those associated with Creutzfeldt-Jakob disease, may not be destroyed by
autoclaving at the typical 134 °C for three minutes or 121 °C for 15 minutes.
Also, some recently-discovered organisms, such as Strain 121 microbes, can
survive at temperatures above 121 °C.
Objective
To prepare sterile nutrient agar for culturing microorganisms
Discussion
Yeasts are chemoorganotrophs, as they
use organic compounds as a source of energy and do not require sunlight to
grow. Carbon is obtained mostly from hexose sugars, such as glucose and
fructose, or disaccharides such as sucrose and maltose. Some species can
metabolize pentose sugars like ribose, alcohols, and organic acids. Yeast
species either require oxygen for aerobic cellular respiration (obligate
aerobes) or are anaerobic, but also have aerobic methods of energy production
(facultative anaerobes). Unlike bacteria, there are no known yeast species that
grow only anaerobically (obligate anaerobes). Yeasts grow best in a neutral or
slightly acidic pH environment.
Yeasts vary in what temperature range
they grow best. The cells can survive freezing under certain conditions, with viability
decreasing over time. In general, yeasts are grown in the laboratory on solid
growth media or in liquid broths. Common media used for the cultivation of
yeasts include potato dextrose agar (PDA) or potato dextrose broth, Wallerstein
Laboratories nutrient (WLN) agar, yeast peptone dextrose agar (YPD), and yeast
mould agar or broth (YM). Home brewers who cultivate yeast frequently use dried
malt extract (DME) and agar as a solid growth medium. The antibiotic
cycloheximide is sometimes added to yeast growth media to inhibit the growth of
Saccharomyces yeasts and select for wild/indigenous yeast species. This will
change the yeast process.
Agar (aka agar-agar from red seaweed)
is a polysaccharide polymer and provides the support structure in the
bacteriological medium. Agar gives a solid support so that bacterial colonies
can form on the surface of the agar medium while allowing the diffusion of
nutrients and water. The structural function of agar in bacteriological media
is similar to the function that gelatin has in Jell-O. In bacteriological
media, agar and nutrients are added together and the specific nutrients are
chosen for the particular type of bacteria you want to grow and for the
conditions under which you want the bacteria to grow. Agar is used rather than
gelatin because agar isn't broken down by most bacteria.
Conclusion
This report has identified on how to
prepare the culture media in the laboratory. It is also identified on what it the purpose of agar in culture media and what is the yeast need for growth. Other than that, the uses of autoclave for sterilization is identify. It is use to avoid contamination and it is works under high steam pressure and temperature.
References
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