**3.2 Nanoparticle characteristics and their influence of antimicrobial activity**

Other factors of the antimicrobial activity, has been sought to analyze what characteristics influence the microbial response to the action of the metal oxide nanoparticles. It is known of existing reports concerning the chemical-physics properties from the metal oxide nanoparticles, but taking into consideration factors like the shape, size, roughness, zeta potential and coatings, etc., that influence the resultant antimicrobial effectiveness [5, 10]. These results could have a mainly therapeutic application in medicine, but it can also be extended to the food industry, to water purification and to the textile industry [28].

#### *3.2.1 Size and shape*

Several reports mention that the size and shape are the most important factors to the antimicrobial activity [23, 29–31]. With respect to size there are findings where this is a crucial factor to damage the bacterial systems for many reasons. The sizes as <30 nm are factors that allows the accumulation and penetration into the bacteria causing damage and consequently leading to bacteria death (<10 nm) [23]. The same authors point out that metal oxide nanoparticles with a size greater than 10 nm promotes the permeability when coming into contact with bacteria [23]. In relation with this, the specific surface area by the nanoparticle size affects the surface to mass ratio affecting on surface reactivity. For this reason, they can also have influence in many direct mechanisms of toxicity against the bacteria and the subsequent loss of viability (**Figure 1**).

With respect to shape, it is by knowing that depending on the synthesis method, it will obtain the form of the nanoparticle [32]. Numerous studies shown various forms obtained like spherical, rod-shaped, truncated triangular, nanotubes, nanorods, nanowires, nanosphere, nanoneedles, nanorings and nanocubic [23, 33, 34]. Evidence reports that needle-shaped metal oxides nanoparticles present higher antibacterial activity than cubic shaped, based on the optical and fluorescence intensity [30].

#### *3.2.2 Surface and zeta potential*

The relation between the surface nanoparticle/nanomaterial and bacterial adhesion has not been fully studied and there are few reports about it. Some studies report that the adsorption of bacterial proteins is promoting by the surface areato-mass ratio carry out the reduction in bacterial adhesion [35–37]. Surface nanomaterials have high degree of roughness, therefore bacteria cell membranes cannot adhere to the surface nanomaterial; so the bacteria adhesion is reduced [10, 38, 39].

The surface charge or zeta potential could be another property of the nanoparticle related with bacteria adhesion since it is important to mention that if the surfaces with negative charge are capable to decrease the interaction with bacteria charged negatively, the surface of nanomaterial with negative charge could obtain the same effect, compromising bacterial adhesion [10, 23, 40]. On the other hand, the electrostatic attraction occurs when the nanoparticles are positively charged promoting the accumulation in bacterial cell membrane, which is negatively charged and then they penetrate inside the bacteria triggering other mechanisms [23] (**Figure 1**).

**19**

these areas.

*3.3.2 Mn3O4 nanoparticles*

*In vitro Antimicrobial Activity Evaluation of Metal Oxide Nanoparticles*

Nanoparticle chemical doping is a modification and functionalization around the surface of nanoparticles to regulate and control the interaction with bacteria and enhance their antimicrobial effect. Reports have shown this method as a factor to improve the presence of surface oxygen atoms that promote the production of reactive oxygen species (ROS) [23]. Similarly, the chemical functionalization increase of the surface-area-to-volume ratio results in increasing the antimicrobial potential activity [38]. Also, this procedure has prevented the agglomeration and

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

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 magne-

Zinc oxide is a compound with excellent antimicrobial properties. It is an n-type

The trimanganese tetroxide, Mn3O4, is a mixed oxide of manganese (Mn (II) Mn (III)2O4) is a normal spinel and crystallizes in cubic form. It occurs in nature as the hausmannite mineral. The antimicrobials properties of Mn3O4 NPs have been little studied. Has been reported an effect of these diseases against strains of *Vibrio cholerae*, *Shigella* sp., *Salmonella* sp., and *E. coli* [45]. The effect of the NPs of Mn3O4 against has been evaluated against *E. coli* and *S. aureus* through microdilution assays [46]. The results of the minimum inhibitory concentration (MICs) indicated that the bacteria *E. coli* was more sensitive to the action

semiconductor with a band gap of 3.3 eV. ZnO NPs can adopt a wide variety of morphologies such as; rings, propellers, belts, wires, among others [41, 42]. The antimicrobial activity of ZnO NPs happens by different mechanisms, one of these is the ROS generation [43] inside the cell. It has been proposed that ZnO NPs can act to generate cell death, or the release of Zn2+ ions, whose excess generates an alteration of cellular metabolism. Some species reported as susceptible to ZnO nanoparticles are; *S aureus*, *S. epidermidis*, *Streptococcus pyogenes*, *Enterococcus faecalis* [44], *Bacillus subtilis*, *Escherichia coli* and *Klebsiella pneumonia* [41]. These bacteria can generate intra-hospital infections causing serious infectious diseases and some strains are found in water or food, so ZnO NPs can have a possible application in

sium oxide (MgO) nanoparticles that have antimicrobial properties.

*DOI: http://dx.doi.org/10.5772/intechopen.84369*

the solubility in different solutions [10].

**3.3 Metal oxide nanoparticles**

accumulations [8, 9].

*3.3.1 ZnO nanoparticles*

*3.2.3 Chemical doping*
