Any food that is not sterilized and sealed can contain disease-causing bacteria  Once sterilized and properly sealed, however, it contains no bacteria  There are many different acceptable food-preservation techniques; each involves either sterilizing and sealing food or else at least slowing the growth of disease-causing bacteria
Some of the techniques may also destroy natural food enzymes that cause food to spoil or discolor quickly
If a food contains no bacteria, then it has been preserved by an acceptable method.