Using a Toxicogenomic Approach to Understand How Silver Poisons the Bacterial Cell

The emergence of the post‐antibiotic era has left us desperate for alternative strategies to combat infectious disease. Historically, silver has been used to prevent and control microbial infections. Silver is now seeing widespread use in a variety of medical devices including bandages, catheters, and endotracheal tubes; as well as numerous household items. Yet, we still don't mechanistically understand how silver poisons the microbial cell. Objectives Recently, our research group demonstrated that the higher oxidation states of silver have an enhanced capacity to eradicate laboratory and antibiotic‐resistant strains of bacteria – both planktonic bacteria as well as biofilms. Our current research objective is to understand the mechanistic details of how silver exerts its toxicity on the bacterial cell. Methodology To address the mechanisms of how silver kills bacterial cells, we used a high‐throughput, toxicogenomic approach ‐ screening a knockout collection of E.coli K12 (the Keio collection) for Ag‐sensitive/resistant mutants. Following our toxicogenomic screen, markerless deletion mutants were generated from statistically significant hits using the Red Recombinase system. The markerless genetic mutants were then subjected to phenotypic and biochemical assays to verify their resistance or sensitivity profile to silver treatment. Results Although silver is thought to exert its toxicity by disrupting thiol metabolism and cellular redox‐status, our results demonstrate that silver poisons E.coli through a variety of previously unestablished mechanisms. These include interfering with genes involved in maintaining cell wall integrity, toxin/antitoxin systems, nutrient catabolism, and quorum sensing. Conclusion Here we demonstrate how a toxicogenomic approach was used to determine the mechanistic manner by which silver poisons the bacterial cell. To that end, the robust nature of this methodology can be used to screen other metals, toxins, and antimicrobials to determine their mechanisms of action. Mechanisms that are desperately needed to develop novel antimicrobial strategies. Support or Funding Information This work has been supported by the Natural Science and Engineering Council of Canada. J.L. is supported by a Banting Postdoctoral Fellowship and an Alberta Innovates Health Solutions Postdoctoral Fellowship Award.