Isolation (microbiology)

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In microbiology, the term isolation refers to the separation of a

Proper isolation techniques of virology did not exist prior to the 20th century. The methods of microbial isolation have drastically changed over the past 50 years, from a labor perspective with increasing mechanization, and in regard to the technologies involved, and with it speed and accuracy.

General techniques

In order to isolate a microbe from a natural, mixed population of living

Traditionally microbes have been cultured in order to identify the microbe(s) of interest based on its growth characteristics. Depending on the expected density and viability of microbes present in a liquid sample, physical methods to increase the gradient as for example serial dilution or centrifugation may be chosen. In order to isolate organisms in materials with high microbial content, such as sewage, soil or stool, serial dilutions will increase the chance of separating a mixture.

In a liquid medium with few or no expected organisms, from an area that is normally sterile (such as CSF, blood inside the circulatory system) centrifugation, decanting the supernatant and using only the sediment will increase the chance to grow and isolate bacteria or the usually cell-associated viruses.

If one expects or looks for a particularly

• If one wants to isolate only a particular group of bacteria, such as
  Legionella species require particular nutrients or toxin binding as in charcoal to grow and therefore media such as Buffered charcoal yeast extract agar
  must be used.
• If one wants to isolate as many or all strains possible, different nutrient media as well as enriched media, such as
  environmental microbiology and food microbiology
  (e.g. dairy testing) to establish the so-called 'aerobic plate count'.

Gram staining allows for visualization of the bacteria's cell wall composition based on the color the bacteria stains after a serious of staining and decolorization steps.^[4] This staining process allows for the identification of gram-negative and gram positive bacteria. Gram-negative bacteria will stain a pink color due to the thin layer of peptidoglycan. If a bacteria stains purple, due to the thick layer of peptidoglycan, the bacteria is a gram-positive bacteria.^[4]

In clinical microbiology numerous other staining techniques for particular organisms are used (acid fast bacterial stain for mycobacteria). Immunological staining techniques, such as

Biochemical testing of bacteria involves a set of agars in vials to separate motile from non-motile bacteria. In 1970 a miniaturized version was developed, called the analytical profile index.

Successful identification via e.g.