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Shocking bacteria to death

Vijay Shankar Balakrishnan

doi:10.1038/nindia.2015.72 Published online 1 June 2015

How the normal bacterial membrane of E.coli (a) is affected when it comes in contact with ZnO nanoparticles (b).

© Arakha, M. et al.

Zinc oxide nanoparticles (ZnO-NPs) can shock bacteria to death using static electricity on their surface, according to a new research1 that promises to have biosafety applications in the nanotech industry.

When bacterial surface comes in contact with the NP surface, the resultant electric play triggers the production of free radicals leading to cell death. 

To test this, researchers at the National Institute of Technology in Rourkela, Odisha synthesized ZnO-NPs with positive (pZnO-NPs) and negative (nZnO-NPs) surface electric potentials. They tested these nanoparticles in cultures of both Gram-positive and Gram-negative bacteria.

The pZnO-NPs greatly slowed down the growth of both types of bacteria, as opposed to the nZnO-NPs. Zeta potential analysis showed that the surface electric charges imparted greater effect against Gram-negative bacteria than Gram-positive bacteria. In general, bacterial surfaces have negative charge potential. But Gram-negative bacteria like E. coli have an additional, negatively charged layer that adds an extra negative charge potential. This causes the difference in the strengths of the activity. 

“We got what we were thinking,” says Manoranjan Arakha, a graduate student and the first author of the study.

The charge neutralisation at the interface between the NPs and bacteria releases energy that triggers the production of free radicals and to release the surface tension in the cell membranes. The cells then leak their contents and lose viability. Using a dye that reacted with the free radicals and stained the surfaces, the team confirmed that all these events were happening at the bacterial cell surface. 

The researchers Manoranjan Arakha (left) and Suman Jha.
Suman Jha, senior author of the study, says electron microscopy and an assay that reports the death of bacterial cells, confirmed that the NPs act like “nanocapacitors” and shock the bacteria to death.

Živilė Lukšienė at the Vilniaus University, Lithuania, says the interesting approach of the NIT team shows how some NPs, not all, exhibit antibacterial activity. “They found new factors which determine the antimicrobial activity of nanoparticles,” she says.

The team is studying the antibacterial effects of other such metallic NPs. They would put the knowledge from this work in treating contaminated drinking water in the local region.

References

1. Arakha M, et. al.The effects of interfacial potential on antimicrobial propensity of ZnO nanoparticle. Sci. Rep.5, 9578. (2015) doi: 10.1038/srep09578