The increase in bacterial resistance to one or several antibiotics has become a global health problem. Recently, nanomaterials have become a tool against multidrug-resistant bacteria. The metal and metal oxide nanoparticles are one of the most studied nanomaterials against multidrug-resistant bacteria. Several in vitro studies report that metal nanoparticles have antimicrobial properties against a broad spectrum of bacterial species. However, until recently, the bacterial resistance mechanisms to the bactericidal action of the nanoparticles had not been investigated. Some of the recently reported resistance mechanisms include electrostatic repulsion, ion efflux pumps, expression of extracellular matrices, and the adaptation of biofilms and mutations. The objective of this review is to summarize the recent findings regarding the mechanisms used by bacteria to counteract the antimicrobial effects of nanoparticles.

This paper reports a comparison of the antibacterial properties of copper-amino acids chelates and copper nanoparticles againstEscherichia coli,Staphylococcus aureus, andEnterococcus faecalis. These copper-amino acids chelates were synthesized by using a soybean aqueous extract and copper nanoparticles were produced using as a starting material the copper-amino acids chelates species. The antibacterial activity of the samples was evaluated by using the standard microdilution method (CLSI M100-S25 January 2015). In the antibacterial activity assays copper ions and copper-EDTA chelates were included as references, so that copper-amino acids chelates can be particularly suitable for acting as an antibacterial agent, so they are excellent candidates for specific applications. Additionally, to confirm the antimicrobial mechanism on bacterial cells, MTT assay (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) was carried out. A significant enhanced antimicrobial activity and a specific strain were found for copper chelates overE. faecalis. Its results would eventually lead to better utilization of copper-amino acids chelate for specific application where copper nanoparticles can be not used.

In recent years, the use and research in nanomaterials have increased considerably. In dentistry, nanomaterials have been investigated in all their specialties like dental prosthesis, implantology, dental operative, periodontics, and endodontics. The nanomaterials are investigated in the areas of dentistry due to their application in the improvement of the physical and chemical properties of conventional materials, as well as the use of the antimicrobial activity of nanomaterials such as silver nanoparticles. Recently, silver nanoparticles (AgNPs) have been studied for their use as an endodontic irrigator due to their high antimicrobial activity. But little is known about the possible mechanisms of the adaptation to AgNPs by endodontic bacteria. These mechanisms may be intrinsic (such as efflux pumps, downregulation of porins, and chromosomal resistance genes) or extrinsic (such as point and adaptive mutations and plasmids with resistance genes) adaptation systems. In addition to this, it has been reported that coselection or coregulation of metal resistance mechanisms, as in the case of nanoparticles, is accompanied by increased resistance to various antibiotics. For these reasons, the objective of this article is to do a review of the literature on the possible mechanisms used by endodontic bacteria to generate resistance to silver nanoparticles and the possible side effects of these mechanisms.

Dental caries is one of the major diseases of the oral cavity affecting humans worldwide. Different alternatives have been used for its control, but its incidence and prevalence are still high. On the other hand, silver has been used for centuries due to its antimicrobial properties. With advances in nanotechnology, the use and research in nanomaterials has increased, recently, and silver nanoparticles have become an essential part of the dental practice, giving materials physical and chemical improvements in their properties, used for their antibacterial capacity preventing and arresting dental caries. The objective of this review was to examine the use of silver nanoparticles, in the treatment of dental caries in the remineralization of teeth hard tissues, as well as the antimicrobial potential, cytotoxicity, and long-term effectiveness.

Nanomaterials obtained by green synthesis technologies have been widely studied in recent years owing to constitute cost-effective and environmental-friendly methods. In addition, there are several works that report the simultaneous performance of the reducer agent as a functionalizing agent, modifying the properties of the nanomaterial. As a simple and economical synthesis methodology, this work presents a method to synthesize silver nanoparticles (AgNPs) using Annona muricata aqueous extract and functionalized with 5-fluorouracil (5-FU). The processes of reduction, nucleation, and functionalization of the nanoparticles were analyzed by UV-Vis absorption spectroscopy, and it was found that they are the function of the contact time of the metal ions with the extract. The structural characterization was carried out by transmission electron microscopy (TEM) and X-ray diffraction patterns (XRD). The antibacterial properties of the synthetized nanomaterials were tested using minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against Enterococcus faecalis, Staphylococcus aureus, and Escherichia coli growth.

Due to the concern to find an alternative to reduce the colonization (microfouling and macrofouling) or the biocorrosion of surfaces submerged for long periods in water, we evaluated the antifouling activity of a commercial paint added with silver nanoparticles (AgNP’s) and copper nanoparticles (CuNP’s), beside copper‐soybean chelate, by electrolytic synthesis, using them in low concentrations (6.94E − 04 mg Ag g⁻¹ paint, 9.07E − 03 mg Cu g⁻¹ paint, and 1.14E − 02 mg Cu g⁻¹ paint, respectively). The test for paint samples was carried out by JIS Z2801‐ISO 22196 for periods of initial time, 6 months, and 12 months, against three bacterial strains of marine origin, Bacillus subtilis, Bacillus pumilus, and Bacillus altitudinis. It was possible to demonstrate, according to the standard, that the sample with the greatest antimicrobial activity was the copper‐soybean chelate against two of the three strains studied (B. pumilus with R = 2.11 and B. subtilis with R = 2.41), which represents more than 99% of bacterial inhibition. Therefore, we considered a novel option for inhibiting bacterial growth with nanoparticles as antifouling additives.