Microbial Cultivation When microorganisms are cultivated in the laboratory, a growth environment called a medium is used. The medium may be purely chemical (a chemically defined medium), or it may contain organic materials, or it may consist of living organisms such as fertilized eggs. Microorganisms growing in or on such a medium form a culture. A culture is considered a pure culture if only one type of organism is present and a mixed culture if populations of different organisms are present. When first used, the culture medium should be sterile, meaning that no form of life is present before inoculation with the microorganism. General microbial media. For the cultivation of bacteria, a commonly used medium is nutrient broth , a liquid containing proteins, salts, and growth enhancers that will support many bacteria. To solidify the medium, an agent such as
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