APMB Topic 1: Microbiological Practices

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General Media

• Used to grow microbes in sufficient quantities

• Classified under: 
  1) Defined
  2) Undefined
  3) Semi-defined

Defined Media

• Known chemical composition

• Generally composed of sugars, ammonia/nitrates and mineral salts, sometimes amino acids and vitamins

Undefined Media

• Unknown chemical composition

• Contain peptones and other additivies with unknown chemical make up

Semi-defined Media

• Chemical composition of most components known

• May contain some peptones

[Defined Media] What is the use of Phosphate salts in medium?

Provide phsophates

Help in buffering pH

[Defined Media] What is the use of Glucose in medium?

Carbon source

[Defined Media] What is the use of Phosphate in medium?

Chelating agent (prevents formation of insoluble magnesium phsophate)

Keeps metal ions soluble 

[Defined Media] What is the use of Magnesium in medium?

essential for growth

[Defined Media] What is the use of Ammonium sulfate in medium?

Nitrogen source

[Undefined Media] What is the use of Bacto peptone in medium?

Source of nitrogen

[Undefined Media] What is the use of Yeast extract in medium?

Provide Nitrogen and Carbon

Provide B group vitamins
- Niacin
- Thiamine
- Vitamin B12

[Undefined Media] What is the use of NaCl in medium?

Encourgaes growth through maintenance of osmotic pressure

Similar concentration ot that in tissues

[Undefined Media] What is the use of Beef extract in medium?

Provides amino acids and vitamins and other growth factors

What is a Chelating agent?

A chelating agent binds to divalent and trivalent cations

Keep metal ions in a solution

What are peptones?

Complex mixture of partially digested proteins

Resuscitation Media

• Used to encourage growth of bacteria damaged during processing

• Broth

• Does not inhibit any microbes

Enrichment Media

• Promotes growth of target microbes/allow wider variety of microbes to grow

• Inhibits growth of non-target microbes

• Broth