22/04/2020
Most people are aware of the element silver. The soft, lustrous metal is cherished for its ornamental value. But fewer are aware that silver is extremely effective at killing microorganisms. In a two-pronged assault, silver increases the permeability of the bacteria's cell membrane and interferes with its metabolism. The dual attacks lead to the overproduction of reactive oxygen compounds, and eventually, cell death.
In their study, scientists Racheli Ben-Knaz Wakshlak, Rami Pedahzur, David Avnir, all based out of the Hebrew University of Jerusalem, killed pathogenic bacteria with silver nitrate, subsequently filtered out the dead bacteria, then placed the dead bacteria in a culture of living bacteria. After six hours, up to 99.999% of the live bacteria joined the ranks of their zombie brethren beyond the grave.
The silver-killed bacteria aren't turning into zombies, of course. The researchers demonstrated that heat-killed bacteria don't kill their live counterparts, but the leftover silver solution used to kill the first bacteria does. This indicates that silver-killed bacteria are simply carrying silver particles that can be passed on to other bacteria. Thus, it would be more accurate to call them deadly land mines of decaying matter. "Zombies" is a bit more poignant, however.
Could this intriguing effect be harnessed in any way? The researchers still aren't sure. For now, their study serves as an interesting demonstration of a cool process that's already occurring.
Source: Wakshlak, R.B.-K., Pedahzur, R. & Avnir, D. Antibacterial activity of silver-killed bacteria: the "zombie" effect. Sci. Rep. 5, 9555; DOI:10.1038/srep09555 (2015).
