**3.3 Metal oxide nanoparticles**

The transition metal oxides (TMO) are compounds with unique electronic properties, most magnetic phenomena involve this type of oxides. The nanostructures formed by TMO, due to their dimensions of a few nanometers and their large surface area, are ideal candidates to interact with bacteria. It is known that NPs of the silver are excellent antimicrobial agents and they are the more studied and reported. However, *in vitro* and *in vivo* studies indicate that nanoparticles based Ag, Cu and Ti are toxic to mammalian cells derived from the skin, liver, lung, brain, vascular system, and also gives rise to a distribution in other organs, where are in accumulations [8, 9].

Therefore, is important that the different metal oxides nanoparticles will be studied and guarantee it clinical use. In particular, there are reports concerning to zinc oxide (ZnO), trimanganese tetroxide (Mn3O4), magnetite (Fe3O4) and magnesium oxide (MgO) nanoparticles that have antimicrobial properties.
