1.
Simple media
Simple media include
the basal media or general purpose media like peptone water, nutrient broth and
nutrient agar which are very commonly used in Microbiology laboratory for
cultivation of microorganisms. Peptone media is prepared using 1% peptone in
0.5% NaCl in water (pH 7.2±0.2). Components of nutrient broth includes peptone,
yeast/ beef extract, sodium chloride and distilled water (pH- 7.2 ± 0.2). When
2% agar is added, it is called nutrient agar. Semi-solid media which is
prepared using same components as that of nutrient agar, but with a different
concentration of agar, is also considered as a simple media. In semi-solid
agar, 0.2 to 0.5% agar is used.
2.
Complex media
Complex
media contain added ingredients for special purposes. It may be for bringing
out certain special characteristics of the organisms or for providing special
nutrients required for the growth of fastidious organisms. Fastidious organisms
are those which are more exacting in their nutritional requirements. Most of
the media other than basal media, used in microbiology laboratory are coming
under complex media. Eg: chocolate agar, Blood agar, MacConkey agar,
Robertson’s cooked meat (RCM) medium, Lowenstein–Jensen (LJ) medium
(Cultivation and isolation of Mycobacterium),
etc. Complex media is also called rich media and typically have a
mixture of many different organic compounds including glucose as carbon source,
a source of amino acids and nitrogen (e.g., beef
and yeast extract), various salts, growth factors, vitamins etc. and water
needed for bacterial growth. This is an undefined medium, because the amino
acid source contains a variety of compounds of which the exact composition is
not known. Meat or beef extract is usually made by hydrolysing natural products
such as meat with enzymes to release monomers like peptone, tryptone etc from
the macromolecules. Another amino acid source yeast extract is made by
extracting small molecules from yeast cells.
3.
Synthetic or Defined media
This
media is prepared using pure chemical substances and does not contain any animal, yeast, or plant tissue or their extracts, hence
called synthetic media. The exact quantity of all ingredients used in the media
is known, hence also called defined media. Synthetic media are used for various
special studies such as for studying the metabolic requirements of the organisms.
This media consists of a defined carbon and nitrogen source, trace elements (Mn,
Mo, Cu, Co, Zn etc.) and vitamins. Glucose or
glycerol is often used as carbon source and ammonium salts or nitrates used as
inorganic nitrogen sources. Dubos’ medium with Tween 80 used for cultivation of
Mycobacterium tuberculosis is an
example of this medium. Minimal media (sometimes called Mineral media)
is also an example of synthetic media. Minimal media contain just enough ingredients, generally without the
presence of amino acids, to support growth of wild type microorganisms. Minimal
media typically consists of a carbon
source (sugar like glucose or less energy source like succinate),
various salts with essential element like Mg, N, P, S which help bacteria to
synthesize protein and nucleic acids and water.
Supplementary minimal media are minimal media that also
contains a single selected agent, usually an amino acid or a sugar. This
supplementation allows for the culturing of specific lines of auxotrophic
recombinants.
4.
Semi- synthetic or Semi- defined media
Semi-synthetic media will be containing a set of
chemical substances of known quantity like the synthetic media, but
differ in that at least some natural ingredients of unknown or variable
composition are also present. A synthetic
medium can be made semi-synthetic by adding a
substances such as yeast extract or beef
extract. Eg: Peptone water which is made up of 1% peptone with 0.5% NaCl in
water
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