Selective & Differential Media

Selective & Differential Media


What is selective media?

Selective media, is made up of certain nutrients that can either inhibit or enhance the growth of certain bacteria. This is why they call it selective media, it is generally only selective for one kind of bacteria or does certain things when that bacteria or fungus is present.

Some examples of selective media include:
* blood agar (used in strep tests), which contains bouvine heart blood that becomes transparent in the presence of hemolytic Streptococcus
* MacConkey agar for Gram-negative bacteria
* Hektoen enteric agar (HE) which is selective for Gram-negative bacteria
* mannitol salt agar (MSA) which is selective for Gram-positive bacteria and differential for mannitol



How about Differential Media?

Differential media or indicator media distinguish one microorganism type from another growing on the same media. This type of media uses the biochemical characteristics of a microorganism growing in the presence of specific nutrients or indicators (such as neutral red, phenol red, eosin y, or methylene blue) added to the medium to visibly indicate the defining characteristics of a microorganism. This type of media is used for the detection of microorganisms and by molecular biologists to detect recombinant strains of bacteria.

Examples of differential media include:
* MacConkey (MCK), which is differential for lactose fermentation
* mannitol salt agar (MSA), which is differential for mannitol fermentation

A more illustration on individual agar;
Macconkeys agar
Mannitol salt agar

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