The good antimicrobial properties of silver make it widely used in food, medicine, and environmental applications. However, the release and accumulation of silver-based antimicrobial agents in the environment is increasing with the extensive use of silver-based antimicrobials, and the prevalence of silver-resistant bacteria is increasing. To prevent the emergence of superbugs, it is necessary to exercise rational and strict control over drug use. The mechanism of bacterial resistance to silver has not been fully elucidated, and this article provides a review of the progress of research on the mechanism of bacterial resistance to silver. The results indicate that bacterial resistance to silver can occur through inducing silver particles aggregation and Ag+ reduction, inhibiting silver contact with and entry into cells, efflux of silver particles and Ag+ in cells, and activation of damage repair mechanisms. We propose that the bacterial mechanism of silver resistance involves a combination of interrelated systems. Finally, we discuss how this information can be used to develop the next generation of silver-based antimicrobials and antimicrobial therapies. And some antimicrobial strategies are proposed such as the \"Trojan Horse\" - camouflage, using efflux pump inhibitors to reduce silver efflux, working with \"minesweeper\", immobilization of silver particles.

The numerous applications of silver nanoparticles (AgNPs) lead to their spread in aquatic systems and the release of silver ions (Ag+), which brings potential risks to environment and human health. Owing to the different toxicity, the mutual transformations between AgNPs and Ag+ has been a hot topic of research. Dissolved organic matter (DOM) is ubiquitous on the earth and almost participates in all the reactions in the nature. The previous studies have reported the roles of DOM played in the transformation between AgNPs and Ag+. However, different experiment conditions commonly caused contradictory results, leading to the difficulty to predict the fate of AgNPs in specific reactions. Here we summarized mechanisms of DOM-mediated AgNPs oxidation and Ag+ reduction, and analyzed the effects of environmental parameters. Moreover, the knowledge gaps, challenges, and new opportunities for research in this field are discussed. This review will promote the understanding of the fate and risk assessments of AgNPs in natural water systems.

Antibiotic-laden bone substitutes represent a viable option in the treatment of bone and joint infections with bone defects. In particular, the addition of silver ions or silver nanoparticles to bone substitutes to achieve local antiseptic activity could represent a further contribution, also helping to prevent bacterial resistance to antibiotics. An in-depth search of the main scientific databases was performed regarding the use of silver compounds for bone substitution. The available evidence is still limited to the preclinical level: 22 laboratory studies, 2 animal models, and 3 studies, with both in vitro and in vivo analysis, were found on the topic. Numerous biomaterials have been evaluated. In vitro studies confirmed that silver in bone substitutes retains the antibacterial activity already demonstrated in coatings materials. Cytotoxicity was generally found to be low and only related to silver concentrations higher than those sufficient to achieve antibacterial activity. Instead, there are only a few in vivo studies, which appear to confirm antibacterial efficacy, although there is insufficient evidence on the pharmacokinetics and safety profile of the compounds investigated. In conclusion, research on bone substitutes doped with silver is in its early stages, but the preliminary findings seem promising.

Healthcare-associated infections (HCAIs) are a major cause of morbidity and mortality worldwide. One of the main routes of transmission is by contact with contaminated surfaces, where nosocomial pathogens form sessile communities called biofilms. When forming biofilms, these pathogens are extremely resistant to antibiotics and standard cleaning procedures. In this regard, in order to eliminate the extent of biofilm formation on these surfaces, intensive efforts have been deployed, particularly in recent years, to develop new antibacterial surfaces containing silver or silver compounds, which can be used to prevent the formation of biofilm. In this review, recent developments in the design and manufacturing of silver-based antibacterial surfaces are described in detail. Up-to-date toxicity and governmental regulations are then extensively presented. Finally, based on current research in this promising field, the main challenges and perspectives for their effective implementation are discussed.

We wish to thank Fewtrell, Majuru, and Hunter for their article highlighting genotoxic risks associated with the use of particulate silver for primary drinking water treatment. The recent promotion of colloidal silver products for household water treatment in developing countries is problematic due to previously identified concerns regarding manufacturing quality and questionable advertising practices, as well as the low efficiency of silver nanoparticles to treat bacteria, viruses, and protozoa in source waters. However, in the conclusion statement of the manuscript, Fewtrell et al. state, \"Before colloidal Ag or AgNP are used in filter matrices for drinking water treatment, consideration needs to be given to how much silver is likely to be released from the matrix during the life of the filter.\" Unfortunately, it appears Fewtrell et al. were unaware that studies of silver nanoparticle and silver ion elution from ceramic filters manufactured and used in developing countries have already been completed. These existing studies have found that: 1) silver ions, not silver nanoparticles, are eluted from ceramic filters treated with silver nanoparticles or silver nitrate; and, 2) silver ions have not been shown to be genotoxic. Thus, the existing recommendation of applying silver nanoparticles to ceramic filters to prevent biofilm formation within the filter and improve microbiological efficacy should still be adhered to, as there is no identified risk to people who drink water from ceramic filters treated with silver nanoparticles or silver nitrate. We note that efforts should continue to minimize exposure to silver nanoparticles (and silica) to employees in ceramic filter factories in collaboration with the organizations that provide technical assistance to ceramic filter factories.