**4.1 Regulatory testing**

*Nanoemulsions - Properties, Fabrications and Applications*

membrane.

*3.3.3 Fe2O3 nanoparticles*

even been determined [51].

*3.3.4 MgO nanoparticles*

of the NPs of Mn3O4. It was observed that the inhibitory effect proportionally increases to the concentration of Mn3O4 NPs, which could divide the different characteristics of the surfaces of the bacterial cells and their interaction with the NPs, therefore the mechanism of action could be focused on the bacterial wall

Iron oxide (III) is a very stable oxide, it crystallizes in hexagonal form and is found in nature as the mineral hematite α-Fe2O3. The nanostructures of this oxide take different forms as they are nanowires, nanotubes, nanospheres, etc. [47]. Although its synthesis has been widely studied, its possible antibacterial effect not. The Fe2O3 NPs bactericidal effect against *E. coli* and *S. aureus* has been reported, where an increase of this effect is observed, as the concentration of iron oxide NPs increases [48]. A bactericidal effect has also been seen on *P. aeruginosa* with a minimum inhibitory concentration of 0.06 mg/L [49]. Another study reports on the bactericidal activity of nanostructured hematite against a variety of Grampositive and Gram-negative bacteria; *P. aeruginosa*, *S. aureus*, *K. pneumoniae*, *Lysinibacillus sphaericus* and *Bacillus safensis* [50]; proposing some mechanisms of action depending on the activity observed in each stage of the growth of the bacteria in question. A bactericidal effect of NPs of Fe2O3 against *S. epidermidis* has

From its properties, its possible application in the remediation of the environment and water, as well as in the biomedical area, has been proposed, due to the

Magnesium oxide is in nature as the mineral periclase [52]. The antibacterial activity of MgO against Gram-positive and Gram-negative bacteria has been reported. It has been proposed that MgO NPs can damage the cell membrane causing the loss of intracellular contents and causing the death of bacterial cells [53]. The generation of reactive oxygen species has been attributed to the surface alkalinity of the MgO NPs [54]. The antibacterial activity of NPs of MgO against Gram-negative bacteria has been evaluated; *E. coli* and *P. aeruginosa* (500 and 1000 μg/mL) and in a Gram-positive bacterium; *S. aureus* (1000 μg/mL) [55]. The MgO NPs potentiated lipid peroxidation induced by ultrasound in the liposomal membrane. In this case the mechanism of action could be associated to the presence of defects, or to the lack of oxygen on the surface of the NP, leading to lipid peroxidation and the generation of reactive oxygen species [55]. The antibacterial effect and mechanism of action of NPs of MgO against strains of *Campylobacter jejuni*, *E. coli* and *Salmonella enteritidis* has been studied [56]. In this case, it was observed that the permeability of the bacteria's membrane, after exposure to the MgO NPs, was compromised, finding the presence of hydrogen peroxide that would subsequently cause cell death. Studies of *P. aeruginosa* and *S. aureus* versus MgO NPs showed a greater zone of inhibition in *S. aureus* than in *P. aeruginosa* [56]. Based on previous work, the authors note that the bactericidal action of MgO NPs may be due to the binding of surface oxygen to bacteria. As the surface area of the particles increases, the concentration of oxygen ions on the surface increases, which results in a more effective destruction of the cytoplasmic membrane and the

different studies of cytotoxicity that have been carried out [47].

**20**

cell wall of the bacteria.

Regulatory agencies require adherence to well established evaluation systems. Regulatory tests applicable to disinfectants, antiseptics or therapeutic antimicrobials vary greatly; and could include to nanoparticles with potential use as antimicrobials.
