VMC 211: General Veterinary Microbiology (1+1)

MEDIA

• Chemically defined medium
  • A medium composed of known chemical compounds. It is also called as synthetic medium.
  • It is needed for cultivation of autotrophs.
  • It is also useful for defining nutritional requirements of heterotrophs.
• For routine cultivation of heterotrophs complex materials like peptones, meat extract and yeast extract are used in the media. Such media support the growth of many heterotyphic bacteria.
• Beef extract
  • It is an aqueous extract of lean beef tissues concentrated to a paste.
  • It contains water soluble substances from animal tissues. This includes carbohydrates, organic nitrogen compounds, water soluble vitamins and salts.
• Peptone
  • It is prepared by digestion of proteinaecious substances like meat,casein and gelatin.
  • Digestion is done by acids or enzymes. Peptone is the principle source of organic nitrogen.
  • Vitamins and carbohydrates may also be present depending on the protein digested.
• Agar
  • It is the complex carbohydrate obtained from certain marine algae. It is used as a solidifying agent for media. Aqueous solution of agar gels when the temperature is reduced below 45 C. It is not source of nutrient for bacteria.Agar is used as a non nutritive solidifying agent to make solid media eg: nutrient broth(liquid) to nutrient agar (solid).
• Yeast extract
  • It is an aqueous extract of yeast cells. It increases nutrient quality.
  • It contains B vitamins and other growth promoting substances.
  • It is a very rich source of B vitamins.
  • It also contains organic nitrogen and carbon compounds.
• Other supplements – blood, serum, extracts of plant or animal tissues. They may be needed for cultivation of some fastidious heterotrophs.
• Some bacteria like Haemophiles  require X (Haematin) & V (NAD) factors additionally.