Microbial strain isolation is the act of isolating a pure strain of bacteria or other microbe from the environment or from a mixed population sample or culture. In medicine, mixed cultures may come from a patient sample such as a throat swab with the goal of isolating and identifying a pathogenic organism. In biotechnology, isolation techniques are used to acquire a pure strain containing the desired genetic modification, when genetic material is purposely added or changed, such as in the generation of recombinant DNA. The purpose of isolation can also be to study the colony morphology of an organism.
The mixed culture is streaked out over the surface of an agar surface to thin out the microbes until individual cells are separated. Individual cells will grow into discrete colony forming units (CFUs) which can be selected for further culture. Some species of bacteria such as Staphylococci can form CFUs from a group of cells rather then from a single cell.
Enrichment culturing is often used for isolating microbial species from soil and marine habitats. Enrichment culture is an isolation technique that makes growth conditions very favorable for an organism of interest and unfavorable for the competition. Enrichment can involve using specific nutrients or environmental conditions to increase the number of the desired organisms to detectable levels. Solid or liquid medium can be used for enrichment culture.
Aseptic Laboratory Techniques: Plating Methods