Professor Dr Günter Klein and Dr Birte Ahlfeld from the Institute of Food Quality and Safety at the University of Veterinary Medicine Hannover (TiHo), with scientists from the Max Planck Society and the Medical Service of the Armed Forces, have investigated how well surfaces that are contaminated with norovirus can be disinfected by using cold plasma. Their results have been published in the online journal mbio.1
Cold plasma is an energetic and highly reactive gas that can be produced at atmospheric pressure. It is currently used in arc welding and in medicine for wound healing. It is formed when a gas such as air is subjected to heat or high voltage energy, creating plasmas.
The plasmas are medically interesting due to their high reactivity. The ions of which they comprise may act upon micro-organisms such as norovirus. Noroviruses are highly contagious and are among the most frequent causes of infectious gastrointestinal diseases. An infection is manifested by sudden violent diarrhoea, nausea and vomiting. Studies from the same group show that noroviruses are transferred via contaminated surfaces such as doorknobs and keyboards. Strong chemicals are commonly used to disinfect the surfaces, but there is a risk that they will damage delicate surfaces. In addition, the bacteria can develop resistance to disinfectants.
'Cold plasma will not harm surfaces or human tissue,' says Klein. 'In addition, the application is environmentally friendly, much faster than with disinfectant and leaves no residue.'
Cold plasma will not harm surfaces or human tissue
The recent study by Klein and colleagues shows that when applying cold plasma, the bacterial count of noroviruses was significantly reduced. 'That surprised us because noroviruses in the environment are very stable,' said Klein. 'They can survive treatment with chlorine or freezing and heating.'
To investigate the effect of the cold plasma on noroviruses, the scientists prepared sterile Petri dishes with various dilutions of a stool sample in which there were noroviruses. They then applied the cold plasma to the samples for different time periods to study the effects. After the treatment, it was found that the samples with the longest exposure time had the lowest bacterial counts.
'As cold plasma can inactivate the virus on the surface tested, we assume that the method could be used for regular disinfection of contaminated surfaces,' said Klein. Even if the pathogens were not completely removed, a reduction in the density and growth is a big step towards reducing the risk of infection for humans.
'A patient infected with noroviruses leaves about 22,000 virus particles when they touch surfaces such as a doorknob. For infection approximately 10–100 virus particles are needed,' said Klein. The cold plasma reduced the number of potentially infectious virus particles after 10 minutes from 22,000 to 1,400. After 15 minutes, only 500 virus particles were present. But even after treatment for only one minute, the scientists observed an effect.
For use outside the lab, the researchers believe the cold plasma generator, which produces the ions could be designed as a handheld device.
In future, Professor Klein and his colleagues want to test the disinfecting properties of the cold plasma on other surfaces as well as with other virus types. They also plan to use electron microscopy to compare the structure of the virus before and after treatment with cold plasma.
1. Inactivation of a Foodborne Norovirus Outbreak Strain with Nonthermal Atmospheric Pressure Plasma 6:1 ; Published 13 January 2015, doi:10.1128/mBio.02300-14
