LAB 3: PREPARATION AND STERILIZATION OF CULTURE MEDIA
INTRODUCTION
Culture media are available as
powders. They require only the addition of water. Nutrients medium is a general
purpose preparation for culturing microorganisms which are not nutritionally fastidious.
The broth contains:
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
15.0 g/L agar powder
The agar has the same composition, except that it
contains 15g/L agar. The final pH of both media is 7.4
Culture media must be stored at the specific temperature, under
specific conditions. All prepared culture media should be stored away from
light and exposure to direct sunlight should be avoided at all the times.
An is an instrument used to sterilize equipment and supplies by subjecting them by high pressure saturated steam at 121 degree celcius for araond 15-20 minutes depending on the size of the load and the contents.
OBJECTIVE
To prepare sterile nutrient agar for culturing microorganisms.
DISCUSSIONS
A widely-used method for heat sterilization is the autoclave. Plant tissue culture media are generally sterilized by autoclaving. The time required for sterilization depends upon the volume of medium in the vessels. Additional sterilizing time is usually required for liquids and instruments packed in layers of cloths, as they may take longer to reach the required temperature. Following
sterilization, liquids in a pressurized autoclave must be cooled slowly to
avoid boiling over when the pressure is released. To ensure the
autoclaving process was able to cause sterilization, most autoclaves have
meters and charts that record or display pertinent information such as
temperature and pressure as a function of time. Nutrient media (agar) that contain thermolabile components can be prepared in several steps. That is, a solution of the heat-stable components is sterilized in the usual way by autoclaving, then cooled to 35-50 degree celcius under sterile conditions: in a seperate operation, solutions of thermolabile components are filter-sterilized.
REFERENCES
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