The good, the bad, and the ugly of metals as antimicrobials

We are now moving into the antimicrobial resistance (AMR) era where more antibiotic resistant bacteria are now the majority, a problem brought on by both misuse and over use of antibiotics. Unfortunately, the antibiotic development pipeline dwindled away over the past decades as they are not very profitable compounds for companies to develop. Regardless researchers over the past decade have made strides to explore alternative options and out of this we see revisiting historical infection control agents such as toxic metals. From this we now see a field of research exploring the efficacy of metal ions and metal complexes as antimicrobials. Such antimicrobials are delivered in a variety of forms from metal salts, alloys, metal complexes, organometallic compounds, and metal based nanomaterials and gives us the broad term metalloantimicrobials. We now see many effective formulations applied for various applications using metals as antimicrobials that are effective against drug resistant strains. The purpose of the document here is to step aside and begin a conversation on the issues of use of such toxic metal compounds against microbes. This critical opinion mini-review in no way aims to be comprehensive. The goal here is to understand the benefits of metalloantimicrobials, but also to consider strongly the disadvantages of using metals, and what are the potential consequences of misuse and overuse. We need to be conscious of the issues, to see the entire system and affect through a OneHealth vision.

Peptides having antimicrobial activity and their complexes with transition metal ions

Peptide antibiotics are produced by bacterial, mammalian, insect or plant organisms in defense against invasive microbial pathogens. Therefore, they are gaining importance as anti-infective agents. There are a number of antibiotics that require metal ions to function properly. Metal ions play a key role in their action and are involved in specific interactions with proteins, nucleic acids and other biomolecules. On the other hand, it is well known that some antimicrobial agents possess functional groups that enable them interacting with metal ions present in physiological fluids. Some findings support a hypothesis that they may alter the serum metal ions concentration in humans. Complexes usually have a higher positive charge than uncomplexed compounds. This means that they might interact more tightly with polyanionic DNA and RNA molecules. It has been shown that several metal ion complexes with antibiotics promote degradation of DNA. Some of them, such as bleomycin, form stable complexes with redox metal ions and split the nucleic acids chain via the free radicals mechanism. However, this is not a rule. For example blasticidin does not cause DNA damage. This indicates that some peptide antibiotics can be considered as ligands that effectively lower the oxidative activity of transition metal ions.