Germ-free organisms are, by definition and title, inherently germ-free. Absolutely squeaky clean, from their skins to their guts to every other part of their insides. Normal organisms have normal gut bacteria and normal epidermal flora. Germ-free organisms have neither. This is what makes them useful for studying bacterial pathogenesis in isolation without interference from endogenous bacteria, or to study how the immune system acts without constant bacterial presence.
Germ-free organisms are tricky to make. First, they do a vasectomy on a male and put it into a cage with a virgin female of fertile age. Then nature takes its course. Mating doesn't result in procreation, but it does result in the female releasing a crapload of eggs (superovulation). Then a hysterectomy is performed on the superovulated female, and the entire uterus is dipped in Allcide to kill anything that might be on it before removing the sterile unfertilized eggs within it. Then purified sperm is added to the eggs, embryos are allowed to form, and then they are frozen. When needed, the embryos are thawed and placed into the womb of a fertile germ-free mother. And if all goes according to plan, germ-free babies are born into a germ-free environment. And thus the germ-freeness of a population continues happily. Of course, once there are enough of both sexes within the germ-free colony, breeding more germ-free organisms becomes a lot simpler. But the whole time, they're living in plastic bubbles.
Here's the thing though, and it really really really really really bothers me: no one seems to know where the first germ-free mother came from or how she was made.