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Common, Enriched, Selective and Differential Media

Cultivation of microorganisms require special medium and conditions.
Such a medium typically comprises of a blend of protein digests (peptone, tryptone) and inorganic salts, solidified by the addition of 1.5% agar.
A culture medium could be solid, semi-solid or liquid broth. Agar is commonly used hardening agent because it is very difficult to breakdown by microorganisms. Silica Gel is also used sometimes.





Based on purpose or application of culture medium it is classified as


1. BASIC CULTURE MEDIUM OR COMMON MEDIUM
It is a common chemfical agar that allow growth of wide range of microorganisms like nutrient agar, tryptic soy agar, and mind heart implantation agar.
It is used for non- fastidious bacteria.
It is used for Standard Plate Count or when nature of microorganism do not matter hugely.
Enriched Media

Sometimes, Basic culture media is not capable enough to grow some fastidious bacteria. When we assume low amount of potential pathogens being present in the specimen, they have to be enriched first, to multiply up the low number – e.g. serum bouillon, dextrose bouillon, chopped meat bouillon
Selective Media

Particular media contain nutrients that restrain the development of a few life forms however enable others to develop. For instance, mannitol salt agar contains a high convergence of sodium chloride that represses the development of most life forms yet allows staphylococci to develop.
Other examples of selective Media
Eosin-methylene blue agar (EMB) as it contains methylene blue, toxic to Gram+ bacteria, allowing only the growth of Gram– bacteria
MacConkey agar (MCK) allow Gram– bacteria bacteria to grow.
Differential Media

Differential media differentiates one type of microorganism with other, based on there biochemical reactions mostly, growing on the same media on a difference in the colony appearance.

Examples of Differential media
Eosin-methylene blue agar (EMB) - Differential for lactose and sucrose fermentation
MacConkey agar (MCK)-  Differential for lactose fermentation

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