Matric No:111356
LAB 3:Preparation And Sterilization of Culture Media
Introduction:
Culture media are available commercially as powders;they require only the addition of water.Nutrient medium is a general purpose preparation for culturing microorganisms which are not nutritionally fastidious.The broth contains:
3.0g/L "Lab-lemco" powder (a beef extract)
2.0g.L yeast extract
5.0g/L peptone (a nitrogen sourse)
5.0g/L sodium chloride
2.0g/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°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 closed when the cell cooler air has been vented.
Steam is continually forced into the chamber until the pressure reaches 103 kPa above atmospheric pressure;at sea level,this pushes the temperature in the chamber to 121°C .The high pressure prevents solution from boiling over at this temperature.Larger volume require longer than 15 minutes to heat up to 121°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.
Result:
A 200mL sterile nutrient is prepared sucessfully.The nutrient medium contain 0.6g "Lab-lemco" powder (a beef extract) , 0.4 g of yeast extract ,5.0g of peptone ,5.0g of sodium chloride and 3.0g agar powder.
Discussion:
1)Beef Extract is derived from infusion of beef and provides an undefined source of nutrients. Beef Extract is a mixture of peptides and amino acids, nucleotide fractions, organic acids, minerals and some vitamins.
2)Yeast extract is rich in vitamins, minerals, and digested nucleic acids.Therefore yeast extract is used in the nutrient medium.
3)Peptone, protein hydrolysates, infusions and extracts are the major sources of nitrogen and vitamins in
culture media.
4)NaCl is generally added to the nutrient media for maintaining the Osmotic pressure. Maintaining osmotic pressure is important, because, increase or decrease in the osmotic pressure leads to cell burst or death due to the effect of osmosis.
5) Agar is used throughout the world to provide a solid surface containing medium. for the growth of bacteria and fungi. Microbial growth does not destroy the gel structure because most microorganisms are unable to digest agar.
Conclusion:
The basic requirement for the growing of microorganisms is carbon sourse,nitrogen sourse,water,suitable temperature and pH.For culturing microorganisms,a sterile nutrient agar is prepared so that the microorganisms can obtain a sufficient nutrient.
References:
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