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Crustacean Compound Fights Bacterial Biofilms

Coating medical devices with it could keep infections at bay, researchers claim

MONDAY, Sept. 11, 2006 (HealthDay News) -- Coating common medical devices with a antimicrobial compound found in crabs and shrimp might fight infection in hospital patients, new research suggests.

A sugar called chitosan, which is found in crustacean shells, seems to protect against the build-up of nasty bacteria and yeast colonies called biofilms. So said scientists in a preliminary report presented Sunday at the American Chemical Society annual meeting, in San Francisco.

"The issue is that we're putting more and more plastic and metal into people as part of medical practice these days -- everything from contact lens to artificial hips and catheters, and a long list of other devices and implants," said lead researcher Philip Stewart, director of the Center for Biofilm Engineering at Montana State University in Bozeman, Mont.

"And so every time you do that there is a chance of having bacteria or yeast colonize that surface and start a biofilm -- groups of bacteria which form a persistent infection," he added. "The contribution we've made here is that chitosan can act to defend a surface from such a microbial challenge."

The bacteria or yeast that constitute a biofilm come from a range of sources, such as a patient's skin or tap water collecting at the point of surgical insertion. Once collected into a slimy, sticky layer of infectious cells, a biofilm is typically highly resistant to standard anti-bacterial treatments -- often requiring surgical removal of the affected device.

Biofilms are at the root of 65 percent of American bacterial infections, and are the leading cause of about 400,000 catheter-insertion bloodstream infections annually, according to the researchers.

Stewart and his colleagues chose to explore the potential of chitosan because of its antimicrobial abilities.

The compound is already sold as a nutritional supplement, and is approved by the U.S. Food and Drug Administration for use in stemming blood loss.

In a lab setting, the researchers used time-lapse fluorescent microscope and dye technologies to observe the behavior of several bacteria and yeast species as they came in contact with a coated surface.

The results, which involved no human or animal trials, suggest the coating helped prevent biofilm formation by, in effect, skewering the incoming microbes. The chitosan sugar molecules functioned like a razor-sharp bed of nails upon which the microbes met their untimely death.

"Now we've known for a long time that chitosans have antimicrobial qualities, so that's not news," said Stewart. "But what's new is the realization that it can actually form a coating that's not just anti-microbial but anti-biofilm, making it harder for the organisms to latch onto the surface and get a hold. And that could provide a real advantage in reducing the infection rate associated with implanted devices."

George O'Toole, an associate professor in the department of microbiology and immunology at Dartmouth Medical School, expressed some reservation as to whether or not the current research team had actually proven its case, but he was enthusiastic about the possibilities.

"This would be a terrific advance if this proved to be true, particularly because there is an advantage in using a non-antibiotic coating that can't be understated," O'Toole said. "Antibiotic coatings in catheters, for example, are a terrible idea because they will likely contribute to the development of [drug] resistance in the long run. So, their non-antibiotic approach is certainly preferred."

"However," he added, "many people have worked on this for many years without -- to my knowledge -- many effective results. So, I would have to see more research."

Dr. Pascal James Imperato, chairman of the department of preventive medicine and community health at the State University of New York Downstate Medical Center in New York City, seconded that opinion.

"It's interesting, but until this type of research is subject to a careful and critical review --which does not appear to have been the case -- we're not really going to know anything about its validity," he cautioned.

"And there are other issues as well, such as what the long-term effects of this kind of coating might be or what the potential resistance could be to these organisms in the future. This is important because one can try to solve one problem, but in the process create others. So, we need much larger and more sophisticated types of studies involving microbiologists, infectious disease specialists and people who are expert in medical devices to confirm the findings."

More information

For additional information on biofilm infections, visit the U.S. Centers for Disease Control and Prevention.

SOURCES: Philip Stewart, Ph.D., director, Center for Biofilm Engineering, Montana State University, Bozeman, Mont.; George O'Toole, Ph.D., associate professor, department of microbiology and immunology, Dartmouth Medical School, Hanover; Pascal James Imperato, M.D., distinguished service professor and chairman, department of preventive medicine and community health, and director, master of public health program, State University of New York Downstate Medical Center, New York City; Sept. 10, 2006, presentation, American Chemical Society annual meeting, San Francisco
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