**1. Introduction**

Infectious diseases are one of the main causes of morbidity and mortality in the world, so there is the need for research on antimicrobial agents. According to the World Health Organization (WHO), resistance to antimicrobials endangers the effectiveness of treatments for an increasing series of infections by bacteria and fungi [1]. In addition, it poses a growing threat to global public health and requires action by all sectors of government, industry, healthcare professions and society. The success of surgery and medical therapy will increasingly be compromised in the absence of effective antibiotics. On the other hand, the dissemination of multidrug-resistant infections will increase the need for laboratory tests and the use of more expensive drugs, thus increasing the cost of healthcare.

In the science of materials, there is an interest in the development of new antimicrobial therapies, capable of fighting opportunistic infections. For this reason, it is important as a first step, to take into account the different laboratory methods that can be used to evaluate antimicrobial activity *in vitro*. The aim of this methods is to detect possible drug resistance in common pathogens [2], but also which are the most appropriate assays to be used in new agents and materials what that have a potential therapy application.

Nanotechnology and tissue engineering are potential applications for the reported antimicrobial properties of nanoparticles (NPs). Some of the potential advantages of NPs, to fight against microorganisms, are that they do not generate resistance and are a safe potential antimicrobial alternative for clinical use [3–5].

However, the research in this area is needed to understand the mechanism of action of NPs and how to design better therapies. In recent years, nanoparticles have been incorporated into the medical field as an alternative to new antimicrobial agents, especially oxides based in silver (Ag), copper (Cu), and titanium (Ti) [6]. On the other hand, findings have raised concerns about their possible toxic effects in humans, triggering an interest to investigate more about the nanotoxicology and the search for new antibacterial nanomaterials with nontoxic properties for human being [7–9].

The antibacterial activity of the NPs depends of the size and shape; so it requires active research of nanometer-scale materials. Recently, basic and applied research has been done on various metal oxides with different shapes and sizes has carried out for their application in a broad scale of areas such as catalysis, in semiconductors, sensors, controlled release of drugs and as antimicrobial agents.

The physical and chemical properties of metal oxide NPs allow their interaction with biological systems, which has become of vital importance due to the increasing resistance of bacteria. Within these properties, there are shape, size, roughness, zeta potential and coatings, among others [5, 10]. The antimicrobial activity presented by the NPs of metal oxides could have a mainly therapeutic application, but it can also be extended to the food industry, to water purification and to the textile industry.

The present chapter will be focused on recent reports that explore the relationships between the use of NPs in the medical field, with an emphasis on their role as antimicrobial agents and the physicochemical properties of metal oxide NPs that influence their antimicrobial response.

Additionally, findings will address antimicrobial activity of novel metal oxides NPs based in zinc, manganese, iron and magnesium. Also, we will discuss diverse methods for the assessment of antimicrobial activity that can have uses for metal oxide NPs and which complies with quality according to official standards to evaluate antimicrobial agents and materials.
