Differential media :
* Media containing reagents or chemical which differentiate growth of one kind of organism for other kinds are known as differential media.
* The common example of differential media are Mac-Conkey's agar, Eosin methylene blue agar and blood agar.
* The contain dyes, reagents or chemicals which allow the observe to distinguish between types of bacterial colonies developed after incubation.
* For examples, if raw sewage is streaked or spread on eosinmethylene blue (EMB) agar some bacteria produce brilliant green colonies, others gummy, pink colonies with dark centres.
* Blood agar medium is a good differential medium.
* If a mixture of bacteria is inoculated on a blood agar medium, some of the bacteria may hemolyse (destroy) the red blood cells while others do not show hemolytic reactions.
* The observer may see a clear zone of hemolyzed red blood cells around certain colonies colonies of bacteria while the non-hemolyzed bacterial colonies do not develop such a clear zone around them.