Examville.com - In Vitro Cultivation Of Bacteria, Types Of Culture Media

In Vitro Cultivation of Bacteria BACTERIOLOGICAL MEDIA is the substrate on which bacterial culture is done and it provides nutrition and pH to the organism Liquid and Solid Bacteriological Media Both are extensively used in bacteriological laboratories. To obtain a pure growth one has to use solid medium because of the following disadvantages with the liquid media: 1. Growth does not show character on the basis of which a tentative diagnosis can be established. 2. If it is a mixed culture of more than one organisms, their separation cannot be performed. However, once a pure growth has been obtained on solid media, liquid media are used to perform further tests because of the homogenous growth in these media. Types of Culture Media Some bacteria can grow with minimum and ordinary available growth conditions whereas many others are very specific in their demands. These can be in liquid or solid state; with or without oxygen. Some media have simple composition whereas others may be either synthetic or complex in composition. Media can be divided into two broad groups: 1. Defined Synthetic Media These are prepared from chemicals and their exact composition is known. These are used for research purposes and are of two types: Simple synthetic media contain a carbon and energy source, an organic source of nitrogen and various inorganic salts in buffered aqueous solution. The complex synthetic media possess, in addition to components of simple media, amino acids, purines, pyramidines and many other growth factors depending upon the nature and growth requirements of the organism.

2. Routine Laboratory Media These media attempt to provide nutrition and pH to the organisms which are akin to that of tissues and body fluids. Many of these nutrients are supplied by aqueous extracts of meat and peptone. There are various types of these media. Name

Purpose

Examples

Basal media

Simple liquid media Base for other media

Nutrient broth, peptone water

Enriched media

Support the growth of nutritionally demanding bacteria

Blood agar, chocolate agar Loeffler's serum slope

Selective media

Suppress growth of unwanted bacteria and encourage desired ones

MacConkey agar Bismuth sulphite agar

Enrichment media

Liquid media and increase number of desired microbes to detectable levels Both functions in same medium Sustain microbes during transportation

Tetrathionate broth, Selenite F Alkaline peptone water

Indicator media

Distinguish colonies of one type from another

MacConkey agar Stuart's medium Cary Blair medium

Storage media

Preserve bacteria

Nutrient agar, Dorset egg media

Selective + Indicator Transport media

MacConkey agar