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Silver seems to help prevent harmful bacteria from spreading by disrupting how they move around.

The precious metal has long been used to stop the transmission of bacteria 鈥� for example, in the filters of some medical face masks and in the antibacterial coatings used on the International Space Station. But until now, one reason it has a sanitising effect had gone unnoticed.

To find out, researchers at the University of Arkansas exposed E. coli to small doses of positively charged silver ions, which are toxic to bacteria. They then used a powerful microscope to watch what happened to the bacteria鈥檚 flagella 鈥� the whip-like motors that bacteria use to move around.

Exposing the bacteria to silver ions stalled their flagella, causing the cells to 鈥渂ecome much, much slower鈥�, says Yong Wang, one of the researchers on the team. These bacteria also changed direction more, so they spent less time moving in a line than non-exposed bacteria.

Silver has been used for decades to stain flagella to make them easier to see under the microscope, says Jim Thomas at the University of Sheffield in the UK. But this is probably the first time its effect on flagella has been studied, he says.

David Coil at the University of California, Davis, says silver won鈥檛 always have this effect because not all bacteria have flagella. But silver stops microbes in other ways too 鈥� for instance, in higher doses, it can and cause bacteria to explode.

Stopping bacteria from moving as easily makes it harder for them to escape and therefore become resistant to silver鈥檚 effects, says Thomas. 鈥淭reatments that work through multiple pathways or targets are much more difficult for bacteria,鈥� he says.

Reference: bioRxiv,

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