Personal Study: Media Types for the Growth of Different
Microorganisms
Why have different media?
Growth media is tailored to the growth requirements of the organism.
Some organisms are fastidious and require a range of specific nutrients
whilst other non-fastidious organisms will grow in relatively simple
media. The media type, format and incubation conditions are chosen
to enhance the growth of a particular or suspected microbe in the
sample.
Media types
Growth media may be liquid (broth) or solid (usually solidified
with agar), which is very resistant to microbial attack and will
not liquefy.
Click on each image below (broth, plates and agar) to find out more
about these media types.
Click on each type of agar plate below for more information
about these.
Classification of agar types
Media, whether in a broth or an agar plate, can be classified into
three main types. These are listed in the table below:
Descriptor
Non-Selective
Selective
Differential
Contain:
Non-specific additives.
Agents that inhibit the growth of microbes other than the
selected one, eg dyes, antibiotics, salts.
Specific ingredients that allow differentiation of colonies
of one organism from another, eg sugars such as lactose.
Support the growth of:
A range of microbes.
A limited or selected range of microbes.
A range of microbes but colonies will be differentiated on
the basis of colour.
Examples:
Nutrient agar (non-fastidious microbes; Horse Blood agar (fastidious
microbes).
Mannitol Salt agar (selective for Staphylococcus spp.).
MacConkey agar (lactose and pH indicator in the media).
