Programmed cell death: the primary bactericidal mechanism induced by copper nanoparticles

Abstract

Copper, a reddish and ubiquitous material in the world, possesses malleable and conductive properties that render copper and its alloys indispensable in vertical integration manufacturing. With advancements in nanotechnology and nanomaterials in recent decades, copper and its related nanoparticles have been engineered. Their applications include engineering, material science, photo−/electro-catalysis, biomedical drug delivery, agriculture, and antipathogen microbicides. Here, we studied the differing toxicity effects of two sizes of copper nanoparticles (CuNPs), recognized for their potent bactericidal properties. Concentration-dependent effects of both 20 and 60 nm CuNPs were significant in Escherichia coli (E. coli), Acinetobacter baumannii (A. baumannii), and Staphylococcus aureus (S. aureus). Sodium dodecyl sulfate, the dispersant of nanoparticles, caused the synergy effects with CuNPs in A. baumannii and S. aureus but not in E. coli. Four modulators were added to CuNP-treated bacteria. By these modulator treatments, programmed cell death was found in E. coli, A. baumannii, and S. aureus. By the BLAST search, caspase-related proteins were commonly identified in gut bacteria and A. baumannii but not in S. aureus. Furthermore, many proteins from E. coli, A. baumannii, and S. aureus were found to harbor the ULK1-catalytic domain. In short, CuNPs can be potent therapeutic agents against bacterial infections.