Metal Based Antimicrobials: Uses and Challenges

In this antimicrobial resistance era, where resistance to most antibiotics is commonplace, metals and metalloid based antimicrobials (MBA) have emerged as an alternative to treat pathogenic agents. A variety of MBAs are under research for their antimicrobial activities, with copper, silver and zinc leading the charge. MBAs are toxic to microorganisms through a variety of mechanisms. Many MBAs attack thiol redox balance and compete out iron in redox enzymes freeing it to carry out Fenton reactions producing reactive oxygen species. Other toxic sites include the cell wall and membrane as well as competing out essential metal transport and their role in essential enzymatic activities. Whether these mechanisms are solely responsible for cell death has yet to be fully elucidated as the majority of molecular mechanistic research has studied specific genes mediating resistance. Still, what is understood is that MBAs demonstrate broad-spectrum activity when compared to conventional antimicrobials. Applications of metals as antimicrobials are concentrated in the biomedical field in the form of: coatings for medical devices, contact-killing surfaces, impregnation of fabrics, among others. Other applications are found in agriculture and industries like food and cosmetics. Novel technologies, like metal-based nanomaterials, metal-organic frameworks, metal-biocide co-crystals and solid metal surfaces, further enlarge the repertoire of metals as a viable alternative against multidrug resistant bacteria. Several challenges lie in the future, including how the current linear-economy model of consumption may eventually lead to a proliferation of resistance to these MBAs. Thus careful stewardship is required, less metals follow the same fate as organic antibiotics.