The medium consists of beef extract or yeast extract , peptone, sodium chloride and agar in case of nutrient agar. Peptone enzymatic digest of animal proteins is the primary source of organic nitrogen, particularly amino acids and long-chained peptides for the growing bacteria.
While sodium chloride maintains the osmotic equilibrium between the microorganisms and the medium, agar acts as a solidifying agent and has no nutritive value. The composition of nutrient agar for mL, mL and 1L are provided in tabular form.
There are other variations for the nutrient media which differ in the quantity of components. The nutrient broth has the same formulation as above, without agar added. Alternatively, the commercially available nutrient broth media powders can be used they are available as a homogenous mixture. Weigh the mixture of contents as prescribed by the manufacturer. If nutrient agar is required, add agar into the nutrient broth after the pH is adjusted and then autoclave.
They can be used up to months. Science direct. Save my name, email, and website in this browser for the next time I comment. The two main types of bacterial growth media used are liquid broth and solid , Jell-o-like agar. Each has specific advantages and disadvantages. The growing environment used will depend on what the researcher wants to do with, or learn from, the microbes.
Nutrient Broth Bacterial Growth Medium. Nutrient broth is typically made of a powdered beef extract that contains peptones broken down proteins. The powder is dissolved in water, put in test tubes, and sterilized. Broth is convenient, as most bacteria will grown in this type of medium, even those with widely different aerotolerances oxygen requirements.
Different Types of Oxygen Requirements of Bacteria. Unlike animals, bacteria do not all require oxygen. Some bacteria are poisoned by oxygen, others can take it or leave it. Liquid broth allows bacteria to grow at varying oxygen levels, since the oxygen available decreases as the depth of the broth increases.
See the test tube diagram below for an illustration of the growth patterns of microbes with different oxygen requirements:.
Obligate anaerobic bacteria , those killed by oxygen, will gather at the bottom of the test tube, staying as far away from oxygen as possible 2. Facultative bacteria , those that can live with or without oxygen, will gather mostly at the top, since aerobic respiration is the most energy efficient way to turn food into energy; but since lack of oxygen does not hurt these microbes, they can survive anywhere in the broth 3.
Microaerophiles gather at the upper part of the test tube but not at the top. These microbes require oxygen, but at concentrations lower than those found in the atmosphere 4. Aerotolerant bacteria are not affected at all by oxygen, so they can be found evenly spread along the test tube 5.
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