I would like to add my two cents in one the topic of electrical charge in the body and the effect of electrical current.
Whether or not the current is AC or DC is irrelevant because the device puts into the body and takes out of the body the same amount of electrons so I am not so sure about the idea that it has some effect on the electrical charge of microbes or cells due to its changing their electrical potential. The electrical current does affect cells and microbes due to the movement of electrons though. Exactly how is mostly a mystery.