Isolation (microbiology)
In microbiology, the term isolation refers to the separation of a strain from a natural, mixed population of living microbes, as present in the environment, for example in water or soil, or from living beings with skin flora, oral flora or gut flora, in order to identify the microbe(s) of interest.[1] Historically, the laboratory techniques of isolation first developed in the field of bacteriology and parasitology (during the 19th century), before those in virology during the 20th century.
History[edit]
The laboratory techniques of isolating microbes first developed during the 19th century in the field of bacteriology and parasitology using light microscopy. 1860 marked the successful introduction of liquid medium by Louis Pasteur. The liquid culture pasteur developed allowed for the visulization of promoting or inhibiting growth of specific bacteria. This same technique is utilized today through various mediums like Mannitol salt agar, a solid medium. Solid cultures were developed in 1881 when Robert Koch solidified the liquid media through the addition of agar[2]
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.
Bacterial and fungal culture[edit]
Inoculation[edit]
Laboratory technicians inoculate the sample onto certain solid agar plates with the streak plate method or into liquid culture medium, depending what the objective of the isolation is:
Bacteria, culture-independent[edit]
While the most rapid method to identify bacteria is by sequencing their 16S rRNA gene, which has been PCR-amplified beforehand, this method does not require isolation. Since most bacteria cannot be grown with conventional methods (particularly environmental or soil bacteria) metagenomics or metatranscriptomics are used, shotgun sequencing or PCR directed sequencing of the genome. Sequencing with mass spectrometry as in Matrix-assisted laser desorption/ionization (MALDI-TOF MS) is used in the analysis of clinical specimens to look for pathogens. Whole genome sequencing is an option for a singular organism that cannot be sufficiently characterized for identification. Small DNA microarrays can also be used for identification.