In order to be able to identify microbial species, it is important to isolate individuals and produce pure (axenic) cultures of each species to be studied.  There are several techniques for the isolation of individual species.

Streak Plates


Streaking for isolation involves separating cells one from another through a series of steps involving passing a sterile loop over a plate of artificial media divided into sectors.  The loop is sterilized between each step, insuring that fewer and fewer cells are passed to each sector.  If done properly, streaking results in the separation of colony forming units (CFUs) of each species.
 

Pour Plates


In the pour-plate technique, CFUs are separated through a process of serial dilution, where small samples of medium containing microbes are sequentially used to inoculate new sterile media.  This reduces the population of cells in each new container by a factor of ten.  Diluted samples are then spread on the surface of solid media and allowed to incubate.  Individual colonies can then be aseptically transferred to sterile media for isolation and study.