Plasma Research at ODU May Be of Value in Prevention of E. Coli Epidemics
Two Old Dominion University researchers have had reason to closely follow news reports of the deadly E. coli epidemic in Germany this spring, especially after the outbreak was traced to contaminated bean sprouts.
Five years ago, a company in Ohio that is a supplier of fresh, ready-to-eat vegetables, contacted ODU electrical engineer Mounir Laroussi to ask if he could use cold plasma technology to kill E. coli on green beans. Laroussi is a leading international expert in the use of cold plasmas for biomedical applications, including germ killing and sterilization.
"The real question was, could E. coli be eliminated without 'cooking' the beans?" he said.
Laroussi collaborated with colleague Wayne Hynes, now the chair of ODU's Department of Biological Sciences and whose specialty is bacteriology, to conduct tests on the bean supplied by the Ohio company. The researchers introduced E. coli to the surface of the beans and then passed them through a plasma chamber.
"I have the e-mail I sent to the company," Laroussi said this week. "It says, 'I have some good news to share with you. We tested the beans with E. coli and we got encouraging results. We were able to get a 3-log reduction of the initial concentration.'" A 3-log reduction means the number of germs remaining after the treatment was 1,000 times smaller.
Laroussi said the company seemed pleased to get the news, but no relationship ever developed between it and the university. "I think there was a personnel change at the company, and the woman with whom I had been in contact may have moved on to other projects," he explained.
"Still, when I heard the recent news from Germany, I kept thinking that this was an interesting coincidence, that we decontaminated beans back in 2006. We should do more research along these lines," Laroussi said.
As it turns out, Laroussi and the ODU Laser and Plasma Engineering Institute that he directs are part of a research consortium that includes the Max Planck Institute in Munich, Germany. Soon after the E. coli outbreak was reported in Germany, Laroussi contacted colleagues there and related information about the tests five years ago at ODU.
Also, Laroussi directed the German colleagues to an article that he and Hynes wrote, also in 2006, reporting their use of a hand-held plasma plume - something like a miniature light saber - to inactivate E. coli colonies in Petri dishes. The article was published in Plasma Processes and Polymers.
Laroussi pointed out that the strain of E. coli that he and Hynes have used for experiments in the past has not been of the pathogenic variety - enterohemorrhagic E. coli, or EHEC - identified in Germany, where at least 30 people have died and hundreds more have been sickened in the epidemic.
In order for the ODU researchers to conduct more experiments with plasma decontamination, Hynes requested early in June from U.S. government disease control authorities a sample of EHEC that would be more similar to the strains that caused the deaths in Germany.
"We have every reason to believe that the cold plasma would be effective against this EHEC, but we want to make sure," Laroussi said. "The problem is, there are a lot of requests from researchers for these samples right now and it may take some time for us to acquire the germs."
In the meantime, researchers at Max Planck Institute were able to obtain five strains of EHEC from a hospital in Munich where patients sickened by the germ were being treated. Dr. Gregor Morfill, a director of research at the institute, told Laroussi by e-mail on June 14 that he and his colleagues performed approximately 100 experiments employing two different devices that emit cold plasmas, one an industrial-type model and the other a hand-held device similar to Laroussi's plasma pencil.
Morfill described the results as "convincing." For example, with a 20-second exposure of cold plasma from the small device, a sample population of EHEC was reduced by 100,000 times.
Laroussi said the German results, together with those obtained by him and Hynes', "give us reason to believe that we could develop, for commercial purposes, a plasma chamber through which sprouts or other vegetables could be passed through and be gently tumbled or rolled to provide full exposure to the plasma."
The ODU engineering professor pointed out that there was news this month of an E. coli outbreak in the U.S., and that in 1997 Virginia was one of two states to report an outbreak of sickness traced to E. coli on alfalfa sprouts. "So this is a problem close to home, as well. We at ODU should definitely be looking for solutions," he said.
Plasmas are a super-excited "soup" that have been called the fourth state of matter - quite different from solids, liquids and gases. Conventional plasmas are radically excited, existing in the cores of stars and in the lightning we see in the skies. At normal atmospheric pressure they can be put to use in neon lights and television sets as long as they are contained in vacuums. These hot plasmas can certainly kill germs on vegetables, but they would also burn up the vegetables.
Cold plasmas are cool to the touch because only the very lightweight electrons in them are excited, and not the heavier nuclei. But for reasons not fully understood, these non-radical plasmas can kill or inactivate certain cells. Experiments have shown them to be useful for sterilization, treatment of disease and wound healing.
Laroussi is best known for the plasma pencil he invented, which shoots out a several-inch plume of the cold plasma. But he also has worked with larger cold plasma devices.
Last year at the International Conference on Plasma Medicine in Germany, Laroussi was one of three researchers worldwide to receive the inaugural International Society of Plasma Medicine Award. Also at that conference, Gayle McCombs, an ODU associate professor of dental hygiene, presented research she has done with Laroussi on plaque-fighting and teeth-cleaning applications of cold plasma.
This article was posted on: June 11, 2011
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