Plasmid preparation is the extraction and purification of plasmid DNA from bacteria for example. Whatever the method used, there are always 3 main steps: cultivation of host organisms (such as bacteria), lysis to recover the plasmids and purification of the plasmid DNA.

There are many kits on the market for making plasmid preparations and these kits are classified according to the volume of culture and the corresponding quantity of plasmids. A distinction is made between Minipreps (for mini-preparation), Midipreps, Maxipreps, Megapreps and Gigapreps.

The mini-prep or Miniprep corresponds to the smallest quantity of plasmid DNA, between 5 and 50 µg for a culture volume of a few millilitres.

The midiprep corresponds to a medium quantity of plasmid DNA, between 100 and 350 µg for a culture volume of 15-25 ml.

The Maxiprep corresponds to a larger quantity of plasmid DNA, between 500 and 850 µg for a culture volume of 100-200 ml.