This proved ideal, for it mixes easily with most compounds, is fairly inert, so does not interfere with biochemical reactions, and once cooled and gelled, it does not liquefy unless subjected to very high temperatures. Over 100 years later agar is still the primary solidifying ingredient in bacteriological media. Since different bacteria require different nutrients, media of various types have been formulated to meet these distinct needs. Adding various indicators, inhibitors, and enhancers allows for morphological species differentiation. Enriched media is used for more fastidious organisms.
Differential media allows for distinguishing different bacteria on the basis of colonial appearance.
The primary use is that of culture storage. One advantage of this agar is that it allows the detection of natural bacterial pigmentation. Chocolate agar - used to grow Neisseria and Haemophilus. This is primarily blood agar which has been heated to cause lysis of the RBCs. Columbia CNA - selective for gram positives.