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The minimum requirements for growth of bacteria include water, a source of carbon, a source of nitrogen, and certain inorganic salts. These are required for synthesis of proteins, enzymes, etc. For example,
o Nitrogen is required for synthesis of proteins, DNA, RNA, and ATP.
o Sulfur is required for certain amino acids and vitamins, and phosphorous is required for nucleic acids, ATP, and phospholipids.
o In addition, inorganic ions, such as potassium, sodium, iron, magnesium, calcium, and chloride are required to facilitate enzymatic catalysis and to maintain chemical gradients across the cell membrane.
Some bacteria grow in a variety of simple media. E. coli and other members of the family Enterobacteriaceae are examples of bacteria that can grow in a variety of simple media contain-ing the inorganic salts and with a source of energy, the simplest being glucose. The inorganic salts in the media provide major essential elements of carbon, hydrogen, oxygen, nitrogen, phos-phate, and sulfur. These chemicals are usually present in the media and are not added specifically.
Some bacteria, such as H. influenzae and other related bacteria, on other hand, are very fastidious and have certain growth requirements. They require certain amino acids, vitamins, and other growth factors that are supplied by adding yeast extract and meat digests to the media. They also require addition of blood or serum for their growth.
Certain lower forms of bacteria even fail to grow in cell-free culture media and require living cells for their growth.
T. pallidumand M. lepraeare two pathogenic bacteria thatcannot grow in any artificial culture media, but can only be cultured when inoculated into living animals.
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