Pulsed field gel electrophoresis

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File:Microbiologist 01.jpg
A microbiologist running a pulsed field gel electrophoresis test used in bacterial typing.

Pulsed Field Gel Electrophoresis (commonly abbreviated as PFGE) is a method for separating large DNA molecules, which may be used for genotyping or genetic fingerprinting.

It is labor intensive and differs from normal agarose gel electrophoresis by the use of an alternating electrical field (hence the name). Under normal electrophoresis, large nucleic acid particles (above 30-50 kb) migrate at similar rates, regardless of size. By changing the direction of the electric field frequently, much greater size resolution can be obtained. The true theoretical basis of this effect is not clearly understood (numerous models have been put forward), but generally speaking, the smaller nucleic acid pieces are able to re-orient to the new field more quickly than are larger ones. This delay in re-orientation means larger pieces end up migrating down the gel slower than smaller, more nimble ones. Frequent changing of the migration direction means that over the entire run, the movement sums to one direction. It is commonly considered a gold standard in epidemiological studies of pathogenic organisms. Subtyping has made it easier to discriminate among strains of Listeria monocytgenes and thus to link environmental or food isolates with clinical infections.

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