Preparation of growth Media for Microorganisms.


The survival of microorganisms in the laboratory as well as in the nature depends on their ability to grow under certain chemical and physical conditions. An understanding of these conditions enables us to characterize isolates and differentiates them into different groups. Such knowledge can also be applied to control the growth of microorganisms in practical situations. A growth media or culture media is a solid or liquid preparation used to growth, harvest and store the microorganisms. To prepare the solid media, solidifying agent i.e. agar is added to the liquid media. Agar is polysaccharide which is extracted from agarophyte red algae, Gelidium amansii. Agar is inert towards microorganisms due to its unique setting, melting temperature and ability to allow diffusion of compounds while interlocking water in the rigid gel. To be effective, the medium must contain all the nutrients which are required for the growth of microorganisms. A wide variety of culture media is employed by the bacteriologist for the isolation, growth and maintenance of pure culture and also for the identification of bacteria according to their biochemical and physiological properties. Generally bacterial culture media can be broadly categorized into the following categories: –

General purpose media: Is a non-selective media which allow most aerobic and facultative aerobic microbes to grow. It is used primarily for the isolation of microorganisms. Media other than general purpose media used are selective media, differential media, specialized media and enriched media etc.

Selective media: Is designed to suppress the growth of some microorganisms while allowing the growth of others i.e. selects for certain microbes. Selective media is usually made in solid from so that individual colonies may be isolated easily. Examples of selective media include Mannitol salt agar, MacConkey agar, Eosin-methylene blue agar, and Columbia C-CAN agar.

Differential media: Allow the growth of more than one microorganisms of interest but with morphologically distinguishable colonies based on specific biochemical properties of the organisms. Most differential media contain a substrate and a chemical indicator, often pH indicator. Examples of differential media are MacConkey agar and Eosin-methylene blue agar.

Enriched Media: It contain specific growth factors needed by fastidious bacteria to support their growth. Examples of enriched media include Blood agar and Chocolate agar.

Composition of NA media:

NA medium that is commonly used to culture members of the Eneterobacteriaceae as well as for coli phage plaque assays.

S. No. Ingredients Quantity[gm/liter]
   1.  Peptone            5.0g
   2. Beef extract            3.0g
   3.    NaCl            5.0g
   4.Distilled    water       1000.0mL

  *For nutrient agar add 15.0 g agar. Used for isolation of bacteria and actinomycetes.

Preparing of Media:

Microbiologists often used multiple types of media to cultivate microorganisms in order to either specifically grows a particular organism, or to obtain information about the biochemical properties of the organisms that grow. The most used culture media to grow the microorganisms is general purpose media [basal media].


  • Ingredients to prepare media
  • Spatula
  • Conical flasks
  • Autoclave
  • Weighing machine


  • Take conical flask and clean it properly.
  • Weight the components of media which you are going to prepare.
  • Add the desire amount of water to dissolve the ingredients of media.
  • Plug in the conical flask with cotton plug properly then autoclave the media at 1210C and 15psi pressure for 15 minutes.
  • After autoclaving, you can use the media for research purpose.


Be sure that the media should be autoclaved properly and it should at 40C until use.

Interpretation of Results:

Media will be seen clear after autoclave.

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