Direct Inoculation (or Direct Inoculation of Culture Media)

Following three culture media are commonly used to perform the tests for sterility:

Nutrient Broth : This medium is used for aerobic microorganisms and have the following features:

The value of redox potential (Eh) of this medium is too high to allow the growth of anaerobes.

The culture medium, such as soyabean casein digest broth, Hartley’s digest broth, only allows the fastidious microorganisms to grow.

Cooked Meat Medium : This medium is used for culturing Clostridia.

Thioglycollate Medium : This medium is used for anaerobic microorganisms, and contains the following ingredients:

Ingredients Purpose
Glucose Energy source.
Sodium thioglycolate Inactive mercury compounds,
Enhance and promote reducing parameters, and
Act as a redox indicator.
Agar Reduces the resultant ‘convection currents’.

Sabouraud Medium : This medium is mainly used for fungal species, and has the following characteristic features:

  1. It is an acidic medium, and
  2. It contains glucose or maltose (a rapidly fermentable carbohydrate).


  1. The three media discussed above should be previously evaluated for their nutritive features, i.e., fertility tests to determine the growth of particular microorganisms.
  2. The three media should also be previously incubated at specified temperature(s).

The direct inoculation method is now discussed under the following three steps:

  1. Quantities of sample to be used,
  2. Test method, and
  3. Observation and interpretation of results.
Read More Topics
Evaluation of efficiency of sterilization methods
Evaluation for bacteriostatic and bactericidal actions
Factors influencing disinfection
Sterilisation of fermentation Air

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Santhakumar Raja

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