IBG Lab Report: LAB 3: PREPARATION AND STERILIZATION OF CULTURE MEDIA

Name : See Yen Shan
Matrix number : 111415

1.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 source)
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 to121°C throughout.After sterilization,the steam pressure is slowly decreased to atmospheric pressure.The sterilized objects can then be removed.

2. Objective

To prepare sterile nutrient agar for culturing microorganisms.

3. Result

A 200mL of culture media is prepared and the culture is sterilized by using aseptic sterilization method which include autoclaving. The sterile medium contains 0.6g "Lab-lemco" powder (a kind of beef extract) , 0.4 g of yeast extract ,5.0g of peptone ,5.0g of sodium chloride and 3.0g agar powder and diluted with water.

4. Discussions

Beef extract powder is derived from fresh beef of healthy animals. Beef extract powder and are used for preparing microbiological culture media. Beef extract may be relied upon for biochemical studies particularly fermentation reactions. The function of these beef extract products can be described as complimenting the nutritive properties of peptone by contributing minerals, phosphates and energy sources. It provides nitrogen, amino acids, vitamins and carbon.
Yeast extract is the water-soluble portion of autolyzed yeast. The autolysis is carefully controlled to preserve naturally occurring B-complex vitamins. Yeast extract is prepared and standardized for bacteriological use and cell cultures, and is an excellent stimulator of bacterial growth. Yeast extract provides vitamins, nitrogen, amino acids, and carbon in microbiological and cell culture media.
Peptone is used as an organic nitrogen source in microbiological culture media for cultivation of a variety of bacteria and fungi. The nutritive value of peptone is largely dependent on the amino acid content that supplies essential nitrogen.
Sodium chloride (NaCl) is widely used in biochemistry and molecular biology applications. It is found in nature, in all body tissue, and is considered an essential nutrient. Used in a wide variety of biochemical applications including creating density gradients, regulating biological functions and as a diluent to increase ionic strength in buffers or culture media.
Agar powder is used throughout the world to provide a solid surface containing medium for the growth of bacteria and fungi. Agar consists of a mixture of agarose and agaropectin, which is derived from a polysaccharide in red algae. Agar is typically sold commercially as a powder that can be mixed with water and prepared similarly to gelatin before use as a growth medium. Microbial growth does not destroy the gel structure because most microorganisms are unable to digest agar and therefore it can be used to measure microorganism motility and mobility as well.
Autoclaving is used to sterilize culture media, instruments, dressings, intravenous equipment, applicators, solutions, syringes, transfusion equipment, and numerous other items that can withstand high temperatures and pressures. The laboratory technician uses it to sterilize bacteriological media and destroy pathogenic cultures. Once the culture media is sterilized then the chances of getting contamination for the growth of bacteria is reduced.