Ingredients of Culture Media
The basic constituents of culture media include the following:
Agar is the main component that is used universally for prepa-ration of solid media. It is obtained from a variety of sea weeds and after necessary processing is usually available as powder or as long shreds. Agar is chiefly composed of:
o A long-chain polysaccharide, consisting of D-galactopyranose units;
o A variety of inorganic salts, minute quantities of protein-like materials, traces of long-chain fatty acids; and
o Minerals, such as calcium and magnesium
Agar is usually used in a concentration of 2–3%. Agar is hydro-lyzed at high temperatures and at high acid or alkaline pH.
Peptone is another important ingredient of culture media. It is a complex mixture of partially digested proteins. It is obtained by digestion of lean meat or other protein materials (such as heart muscle, casein, fibrin, or soya flour) with proteolytic enzymes (such as pepsin, trypsin, or papain).
Other common ingredients of media include water, sodium chloride and other electrolytes, meat extract, yeast extract, malt extract, blood, and serum. Meat extract is available commercially as Lab-Lemco and contains inorganic salts, carbohydrates, certain growth factors, and protein degradation products. Blood or serum is usually used for enriching culture of bacteria. Usually, 5–10% defibrinated sheep or human blood is used.