Aim
To prepare nutrient agar plates for cultivation of
bacteria.
Principle
Nutrient Agar is a
basal solid medium which support the growth of a variety of common
heterotrophic bacteria. It is one of the general purpose media. It is used for
the isolation of mciroorganisms and to do some sensitivity tests. The pH of the
medium is 6.8-7.2. The neutral range of pH range aids the growth of a wide
variety of microorganisms. The nutrient agar media consists of:
Peptones- They
are protein hydrolysate prepared by partial proteolytic digestion of meat,
casein, soya meal, gelatin and other protein sources. They serve as source of
carbon, energy and nitrogen.
Beef Extract- They
are prepared by extracting water soluble components of beef tissues. It is a
complex mixture of proteins, carbohydrates, lipids and other biochemical
constituents.
Yeast Extract- An
aqueous extract of yeast cells containing vitamins and other growth factors.
Agar agar- A
complex polysaccharide extracted from the algae Gellidium. It is a solidifying
agent with gelling temperature of 45oC and melting temperature of 95oC.
It is not a nutrient source and is resistant to enzymatic dehydration.
Beef extract,
Yeast extract, peptone, sodium chloride, agar agar, distilled water, conical
flask, weighing machine, measuring cylinder, heater.
1. Beef extract,
yeast extract, peptone and sodium chloride were weighed to the required amount
and added to a known volume of water.
2. They were mixed
well and dissolved.
3. pH was adjusted to
6.8-7.2.
4. The agar was
weighed and added to the medium and dissolved by boiling.
5. After the agar was
dissolved properly, the medium was poured to conical flask or tubes in the
required amount.
6. These were plugged
with cotton and autoclaved at 121oC at 15 lbs pressure for 20
minutes.
7. The medium was
then cooled to hand bearable temperature and poured into sterile petri plates.
A nutrient agar plate was prepared.
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