Culture medium or Growth medium

                                              Definition  

A liquid or solid preparation made for the growth, storage, or transport of microorganisms or other types of cells such as animal or plant cells. 

A growth medium or culture medium is a liquid or gel designed to support the growth of microorganisms or cells, or small plants like the moss Physcomitrella  patens.

History-

• Robert Koch (1843-1910) could be considered the father of culture media.

• His first success in bacteriology was in the isolation of Bacillus anthracis which at the time was causing the disease anthrax in cattle.
• This was the first time that any pathogenic organism had been isolated and studied outside of the host's body.
• It was after this discovery that Koch wrote his famous postulates regarding the causative agents of infectious disease, which were published in 1882:
1. The organism must be consistently associated with the disease.
2. It must be isolated and grown in pure culture.
3. The pure culture must be shown to induce the disease when injected into experimental animals.
• Although Louis Pastuer (1822-1895) and Koch are both considered to be responsible for the establishment of the science of microbiology, Koch and his coworkers systematically identified all the agents of the major bacterial infectious diseases of the 19th century.

Requirements-

 A microbiological culture medium must contain available sources of:
• Carbon
• Nitrogen
• Inorganic phosphate and sulfur
• Trace metals
• Water
• Vitamins

Cultivation of microorganisms depends on a number of important factors:

 Proper nutrients must be available.

 Oxygen or other gases must be available, as required.
 Moisture is necessary.
 The medium must have an appropriate pH.
 Proper temperature relations must prevail.
 The medium must be free of interfering bioburden.
 Contamination must be prevented.

CONSTITUENTS	SOURCE
Amino-Nitrogen	Peptone, protein hydrolysate, infusions and extracts
Growth Factors	Blood, serum, yeast extract or vitamins, NAD (Nicotinamide adenine dinucleotide)
Energy Sources	Sugar, alcohols and carbohydrates
Buffer Salts	Mineral Salts and Metals
Mineral Salts and Metals	Phosphate, sulfate, magnesium, calcium, iron
Chemicals, antimicrobials and dyes	Chemicals, antimicrobials and dyes
Indicator Dyes	Phenol red, neutral red
Gelling agents	Agar, gelatin, alginate, silica gel

Media ingredients -

PEPTONE, PROTEIN HYDROLYSATES, INFUSIONS

AND EXTRACTS –

                                    Are the major sources of nitrogen and vitamins in culture media. Peptones are water-soluble ingredients derived from proteins by hydrolysis or digestion of the source material; e.g., meat, milk.

CARBOHYDRATES-are employed in culture media as energy sources and may be used for differentiating genera and identifying species.

BUFFERS- maintain the pH of culture media.

SELECTIVE AGENTS-include bile salts, dyes and antimicrobial agents.

• Bile salts and desoxycholate are selective for the isolation of gram-negative microorganisms,               inhibiting gram positive cocci.

DYES AND INDICATORS -are essential in the preparation of differential and selective culture           media.

• In these formulations, dyes act as bacteriostatic agents or indicators of changes in acidity or                alkalinity of the substrate.

ANTIMICROBIAL AGENTS are used in media to inhibit the growth of bacteria, yeasts and fungi.

SOLIDIFYING AGENTS, including agar, gelatin and albumin, can be added to a liquid medium in    order to change the consistency to a solid or semisolid state.