Nanoparticle bactericidals overcome the problem of antibiotic resistance © Getty 
Metal nanoparticles owe their bactericidal effect to small size and high surface to volume ratio. This led the researchers to explore the antibacterial activities of silver and copper nanoparticles. They prepared silver and copper nanoparticles by running chemical reactions between nitrate salts of silver and copper and sodium borohydride. Then they tested the bactericidal effect of the nanoparticles against four strains of Escherichia coli, one strain of Bacillus subtilis, and three strains of Staphylococcus aureus in plates and liquid batch cultures.
The study found that both E. coli and S. aureus showed higher sensitivity to the silver nanoparticles compared to copper nanoparticles. On the other hand, B. subtilis showed greater sensitivity to copper nanoparticles. The researchers say that the nanoparticles release ions of silver and copper in culture medium. The metallic ions attach themselves to the negatively charged bacterial cell wall and rupture it leading to cell death.
For E. coli (strain ATCC 10536) and S. aureus (strain ML 422), silver nanoparticles demonstrated greater bactericidal efficiency as compared to penicillin.
"These nanoparticles have great promise as antimicrobial agents," says lead researcher Suparna Mukherji. Combination of silver and copper nanoparticles may provide a wholesome bactericidal effect against mixed bacterial population, she adds.
