Lab 3 report prepared by Teoh Leong Sin

Name : Teoh Leong Sin
Matric No : 111433

Introduction

Culture media are available commercially as powders; the require only addition of water. Nutrient medium is a general 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.
     Autoclaving is a process that use moist heat and pressure so that all parts of the material to be sterilized reach 121 degree C for 15 minutes. An autoclave is, in essence, a large pressure cooker; a chamber which may be sealed off against surrounding air. Materials for sterilization are placed in the chamber, the door is sealed, and pressurized steam is forced into the chamber. The incoming steam displaces cooler air through an exhaust valve; this valve closes when the cell cooler air has been vented.
     Steam is continually forced into the chamber until the pressure reaches 103kPa above atmospheric pressure; at sea level, this pushes the temperature in the chamber to 121 degree C. The high pressure prevent solutions from boiling over at this temperature. Larger volumes require longer than 15 minutes to heat up to 121 degree C throughout. After sterilization, the steam pressure is slowly decreased to atmospheric pressure. The sterilized objects can then be removed.


Objective

To prepare sterile nutrient agar for culturing microorganisms.


Discussion
1) Precaution steps of preparing culture medium
-weigh appropriate amount of broth and then mix it into a beaker. After that, add 200mL of distilled water into the beaker 
-heat up the solution and stir it by using a rod to let the culture medium completely dissolve
-After boil,pour the culture medium into Scott bottle and loosely recap the bottle.
-Sterilize the culture medium by using autoclaving method
- After sterilization, the steam pressure is slowly decreased to atmospheric pressure. Scott bottles is removed from the autoclave machine and cooled it in laminar air flow cabinet




2) Autoclaving method
-a most effective and most efficient method of sterilization.
-culture medium steamed under high pressure at a standard temperature of 121 degree celcius for 15 minutes.

-time to autoclaving depend on the volumes of culture medium.

-when proper condition and times are employed, there are no living organisms will survive.

3) Laminar flow

-physical containment devices that act as primary barrier to protect from contamination and infection 

-horizontal-flow clean bench and biological safety cabinet

-Horizontal laminar flow use a high effiency particulate air (HEPA) filter and blowers that generate a non-mixing stream of air 

-Vertical laminar flow(biological safety cabinet)  are used for work with low-risk substances and materials, when protection of working material from environment is required or work with item requires a sterile working zone. Cabinets are used for equipment of local workplaces in medical, pharmaceutical and other institutes with high requirements for air cleanliness in the working zone.

 Conclusion

The best way of sterilization is autoclaving, it can completely inactivate all microorganism  in the medium. 

References

http://en.wikipedia.org/wiki/Autoclave 

http://www.ehow.com/how_4913374_use-autoclave.html

http://en.wikipedia.org/wiki/Laminar_flow_cabinet

http://www.terrauniversal.com/laminar-flow-hoods/vertical-laminar-flow-hoods.php