The key to antibiotic resistance has focused almost entirely on evolution at the genetic level. Because of the incredible speed at which bacteria multiply and divide, evolution can occur in a matter of days. There are several means to accomplish this; at the simplest mechanistic level, DNA is altered allowing for the rise of a resistant version of a protein targeted by antibiotics. Once this evolution occurs, future generations will be able to resist treatment. Add enough of these various moments of evolution and a bacterium can become multi- or extremely-drug resistant or, in some cases, pan resistant, in which no antibiotic treatment is effective.