Double strike for hospital bacteria

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Photo by Karolinska Institute

Researchers at the Swedish Medical Nanoscience Centre at Karolinska Institutet have developed a new defence in the battle against the cross transmission of microbes from plastic surfaces in hospitals. The team, led by Professor Agneta Richter-Dahlfors, showed that by zapping the bacteria with a combination of an innovative way silver nanoparticles and a small electrical current, bacterial growth on these surfaces could be wiped out.

The method, which could prove to be useful in preventing bacterial infections in hospitals, is presented in the scientific journal Advanced Healthcare Materials.

Contamination often occurs from hands – both as a result of direct patient contact as well as from touching surfaces and equipment - and hospital wards are full of plastic surfaces with many hand-touch sites. These include plastic tubes, equipment for monitoring and support and other devices, each of which potentially harbouring dangerous microbes. Bacteria are able to survive up to months on dry plastic surfaces, and longer under humid or low-temperature conditions. They can then spread to patients and cause infections.

While both large electrical currents and high silver concentrations are known to kill bacteria, they also pose a risk to humans, which is why their use in hospitals is limited. This new research shows that it is not necessary to use dangerous concentrations of silver or large currents to kill bacteria, if these are used in combination.

According to Agneta Richter-Dahlfors, the idea was that by targeting the bacteria on several fronts at the same time, the effect of different small attacks becomes larger than when each factor is acting on its own.

 “It’s a phenomenon known as the bioelectric effect, whereby electrical fields weaken bacterial cells against external attacks”, says PhD student Salvador Gomez-Carretero at Karolinska Institutet's Department of Neuroscience. “We use electrical signals to increase the antimicrobial activity of the silver nanoparticles. This reduces the amount of silver needed, which is beneficial for both the patient and the environment.”

The research team focussed on the notorious hospital pathogen Staphylococcus aureus.

They found that applying tiny electrical currents to a conducting plastic surface had no effect on bacterial growth. On a similar surface exposing an attached layer of silver nanoparticles, bacterial growth was reduced. However, application of a tiny electrical current to the latter surface enhanced the effect of attached silver nanoparticles, and the bacteria were completely destroyed.

The study was financed by the Swedish Research Council, Vinnova, Carl Bennet AB and the Swedish Medical Nanoscience Centre.


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