PREPARATION AND STERILIZATION OF CULTURE MEDIA
INTRODUCTION
Microorganisms are available in all places and surrounding
environment and it is difficult to us to find their original habitat. So, in
order to cultivate the microorganisms, the factitious condition in laboratory
is created. A culture medium is a liquid or gel that designed to support the
growth of microorganisms or cells. In the other hand, culture media are
available commercially as powders which they are only required the addition of
water. There are many different types of media and the most common culture
media for microorganisms are broth and agar. The contains for broth are :
·
3.0 g/L “Lab-lemco” powder (a beef extract)
·
2.0 g/L yeast extract
·
5.0 g/L peptone ( a nitrogen source)
·
5.0 g/L sodium chloride
·
2.0 g/L agar powder
For agar, it also has the same composition as broth except
that it contains 15 g/L agar. Final pH for the both media is 7.4.
To sterilize all
parts of the material, autoclave process is needed. Autoclave process used
moist heat and pressure to sterilize the materials at 121 ͦC for 15 minutes. But, it is depending on the size of the load
and the contents. An autoclave is like a large pressure cooker which have a chamber and the chamber have to
be sealed off against surrounding air. Materials that have to be sterilize must
be placed in the chamber, sealed the door and pressurized steam is forced into
the chamber. The steam will displaces cooler air through an exhaust valve. Steam
will continually forced to the chamber until it reaches the pressure 103
kPaabove the atmospheric pressure and this will increase the temperature to
121˚C. The high pressure will prevents the solutions from boiling over at this
temperature. Longer than 15 minutes is required when the volume is larger to
heat up to 121˚C. The steam pressure can be decreased slowly to atmospheric
pressure when the sterilization process finished and then the sterilized objects
can be removed.
 |
Figure 1
: autoclave machine
|
OBJECTIVE
·
To prepare sterile nutrient agar for culturing
microorganisms.
DISCUSSION
There are several steps in preparing the culture medium. Firstly,
cleaned the pan and inside of the balance with brush. This step must be done before
weighing the culture medium powder because to avoid the error during reading
the weigh. Then, put the container onto the balance and press “tare” button to
get the accurate reading. In the other hand, distilled water is measured by
measuring cylinder. Make sure that do not pour all the water into the beaker
because it should be some distilled water have to be reserved to washing the
leftover powder from the weighing container to the beaker. After that, to make
sure the correct composition of culture media is produced, the correct amount
of water is added. Then, stirred the media by using rod to ensure that the
media dissolved fully in water. Next step is put the entire medium into the
Scott bottles. Labelled the bottles and loosen the cap of the bottles before
put it into the autoclave machine. This is because autoclave works under the
high steam pressure and loosen the cap will allow the expansion of the bottles
and the bottles will not break. After autoclave, Scott bottles is removed and
the cap is tightened. The bottles should be turned overagain for a few times so
that no agar will solidifyat the bottom of the bottles. This is to make sure
that the culture agar can be used for the pour-plate in the next laboratory.
CONCLUSION
This report has identifed on how to prepare the culture media in
the laboratory. Commercial nutrient agar is used because it prepare suitable
medium for microorganisms growth. Then, sterilization process is required to
culture the microorganisms in the nutrient agar in order to avoid the
contamination. Autoclave process also used in this preparation for sterilize
the nutrient agar and it is works under the high steam pressure and
temperature.
REFERENCES
No comments:
Post a Comment