INTRODUCTION
A culture
media is special medium used in microbiological laboratories to grow different
kinds of microorganisms. A growth or a culture medium is composed of different
nutrients that are essential for a microbial growth.
Since
there are many types of microorganisms, each having unique properties and
requiring specific nutrients for growth, the culture media are of many types
based on what nutrients they contain and what function they play in the growth
of microorganisms.
A
culture may be solid or liquid. The solid culture media is composed of a brown
jelly like substance known as agar. Different nutrients and chemicals are added
in it to allow the growth of different microorganisms.
culture media
culture media
An autoclave is
an instrument used to sterilize equipment and supplies by subjecting them to
high pressure saturated steam at 121 °C or more, typically for 15–20 minutes
depending on the size of the load and the contents.When microbiological media
has been made, it still has to be sterilized because of microbial contamination
from air, glassware, and hands. Within a few hours there will be thousands of
bacteria reproducing in the media so it has to be sterilized quickly before the
microbes start using the nutrients up. The sterilization process is a 100%
kill, and guarantees that the medium will stay sterile unless exposed to
contaminants by less that adequate aseptic technique to exposure to air.
Media
sterilization is carried out with the autoclave, basically a huge steam cooker.
Steam enters into a jacket surrounding the chamber. When the pressure from the
steam is at a certain point in the jacket, a valve allows the steam to enter
the chamber. The pressure will go up over 15 pounds per square inch (psi): at
this point the timer begins to count down---usually for 15 minutes, depending on
the type of media. The high pressure in a closed container allows the
temperature to go above the highest temperature one could get by just boiling,
around 121 degrees C. Therefore, the parameters for sterilization with an
autoclave are 121 C at >15 psi for 15 minutes. Fifteen minutes is the
thermal death time for most organisms (except some really hardy sporeformers).
An autoclave
OBJECTIVE
To prepare
sterile nutrient agar for culturing microorganisms.
DISCUSSION
The culture media are prepared by weighing as below ;
0.6 g/L “Lab-lemco”powder (a beef extract)
0.4 g/L yeast extract
1.0 g/L peptone (nitrogen source)
1.0 g/L sodium chloride
3.0 g/L agar powder
Beef extract
Peptone
Sodium chloride
Agar powder
Here are
many steps to be taken in the process of preparing culture medium. We cleaned
the pan and inside of the balance with a brush before we weigh culture medium
powder so that it is free from anything on or around its surface that can
affect our readings. The “tare” button can only be pressed after the container
is put onto the balance to get the accurate reading. In addition, the distilled
water was measured using measuring
cylinder. The water should not pour all into beaker, because there should be
some distilled water reserved for washing of leftover powder from the
weighing container into beaker. The
correct amount of distilled water is added to make sure we produce the correct
composition of culture media. After the distilled water is added to the culture
medium powder, we used rod to stir the media so that all powder from culture medium dissolved in water. Then,
the entire medium has been poured into Sccott bottle and loosen the cap of the
bottle before putting into the autoclave machine. Autoclave works under high
steam pressure. Therefore, we loosen the cap to allow the expansion of the
bottle so that the bottle will not break. After autoclaving, the Scott bottle
was removed from the autoclave machine and the cap of the bottle is tightened.
The bottle should be turned over again for a few times so that no agar will
solidify at the bottom of the bottle. This is to make sure that the culture
agar can be used for the pour-plate in the next laboratory work.
Conclusion
This report
identified the correct ways to prepare culture media and culture media was
prepared successfully.
Autoclaving is
the most effective and most efficient means of sterilization.
Reference
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