Systematic Veterinary Bacteriology and Mycology

INTRODUCTION

• It is not always possible to identify organisms by microscopy alone.
• Only after growing them and isolating them in pure culture, it is possible to identify them.
• Robert Koch used boiled potato slices for preparation of solid media.
• Later he used ‘gelatin’ and then “Fannie Eilshemius Hesse” introduced “agar-agar” or ‘agar’ as a base for preparing solid media.
• Bacteria very considerably in their nutritional requirement and over 7000 culture media have been devised.
• The basic requirements of the culture media are,
  • It should have energy source.
  • It should have carbon source.
  • It should have nitrogen source.
  • It should have salts such as sulphate, phosphates, chlorides, K, Na, Fe, Ca and Mg and trace elements such as Mn, Mo and Cu.
  • It should have a satisfactory pH of 7.2 – 7.6.
  • It should have as “Redox Potential”. Redox potential is the intensity level of oxidizing or reducing condition in a system by the readiness of the all components in that system to take up or release electrons. It is measured in “Mille volts”.
  • It should have growth factors.

Examples:

• Tryptophan for Salmonella.
• ‘X’ and ‘V’ factors for “Haemophilus”.
• Common ingredients used in the medium are agar, blood, serum, yeast extract, peptone, beef extracts etc.

Agar

• Agar is prepared from varieties of seaweeds and mostly contains long chain polysaccharides (galactose).
• It also contains various amounts of inorganic salts and protein like substances.
• It melts at 90-100^oC and usually solidifies at 40^oC depending on agar concentration.
• A completely solid medium requires an agarose concentration of 1.5 – 2%.

peptone

• It is a compound mixture of partially digested protein and is a source of organic carbon.
• It contains polypeptides, amino acids and a variety of inorganic salts including phosphates of potassium and magnesium and growth factors.