>>9822335Numerous chromogenic agar exist on the market for bacterial growth and to enhance identification.
These usually involve a substrate which when lysed in the presence of a metabolic by-product of a specific bacterial isolate will cleave that substrate releasing a reporter dye so causing the characteristic colour change in colonies.
There are other agar media on similar principles such as CLED agar which differentiate bacteria on the principle of whether they metabolise lactose or not.
As another example for salmonella differential a good agar to use is XLD agar which distinguishes salmonella sp. from other enteric pathogens.
I'm no sure if there exist agar which change colour over a maturation period i.e it will change to one colour and then subsequently another, but it very possibly may exist though I'm not aware of it.
Go look on OXOID or Biomerioux website to see their selection of agar mediums for diagnostic use.
