Imagine food processing machines with surfaces that kill harmful germs on contact. Or surgical devices that prevent staph and strep infections among patients recovering from surgery. Or an insulin nasal spray replacing injections in the daily lives of diabetics.
These wonders and more are possible thanks to nisin.
Okay, it's not exactly a household word. You won't find it in the dictionary, although an Internet search engine turned up 956 references. But this powerful germ fighter has applications in food processing and medicine that show great promise.
Oregon State University researchers found that coating food processing equipment with nisin can help prevent outbreaks of food poisoning. The same coating on catheters and other surgical devices may reduce the number of post-operative staph and strep cases in hospital intensive care units.
Moreover, research on nisin now underway at OSU may allow diabetics to take their daily dose of insulin with a nasal spray rather than a hypodermic needle. And nisin may remove a roadblock to testing the effectiveness of anti-cancer drugs. Nisin is one of a group of substances known as bacteriocins-another word you may encounter in the news more frequently. Bacteriocins are proteins generated by bacteria. Scientists are interested in them because of their ability to destroy bacteria, including those that cause deadly outbreaks of food poisoning such as Listeria monocytogenes, Clostridium botulinum and E. coli 0157:H7.
"Nisin is produced by the same dairy bacteria that produce cheese and yogurt. It's a protein that kills other bacteria," said Mark Daeschel, a microbiologist in OSU's Department of Food Science and Technology and Agricultural Experiment Station researcher.
Discovered in 1928, nisin was at first thought to be a conventional antibiotic. Only later was it fully identified, and in the late 1950s, food processors in Europe and Africa began putting it in foods such as processed cheese spreads and dairy products as a preservative. It wasn't used in the United States until 1988, when the Food and Drug Administration approved its use in a narrow range of foods.
Daeschel and another Experiment Station researcher, Joe McGuire, a professor in the OSU Department of Bioresource Engineering, were well aware of nisin's reputation. But rather than incorporating it in foods, they wondered if it could prevent harmful bacteria from growing on food processing equipment, a major problem that continues to plague the food industry.
"Foodborne disease is often spread by cross-contamination between foods and unclean surfaces on food manufacturing equipment," said McGuire, whose research interests focus on the interaction of proteins on solid surfaces.
Bacteria and spores that cause disease and spoilage can stick to the surface of machinery, he explained. Once attached, they eventually build up a layer on the surface that is called a biofilm. Dental plaque, for example, is a biofilm. Bacteria in the mouth attach to the teeth and eventually form a thick layer of bacterial products that attacks the tooth enamel and causes tooth decay.
Once established on food manufacturing equipment, a biofilm can become a health hazard by harboring disease-causing bacteria that can be shed into food as it is being processed.
Where does nisin fit into the picture? The presence of protein, such as nisin, on a solid surface affects the ability of bacteria and other cells to stick-or adhere-to that surface. It can, for example, prevent bacteria from sticking to a surface. Or, on the other hand, it can also make it easier for bacteria to get established and colonize a surface.
When a mixture containing protein comes in contact with a surface, the protein tends to gather in a condensed layer-a process called adsorption. "We knew that nisin likes to locate at surfaces. If you dissolve it in a liquid, it will rapidly coat the inner wall of the container," said McGuire.
"We wanted to know what would happen if we coated a surface with nisin," said Daeschel. "Would it form a barrier to bacteria the same way anti-fouling paint prevents barnacles from attaching to the hull of a ship?" Moreover, Daeschel explained, it's easier to prevent a biofilm from getting established in the first place than to deal with it after it's there.
With funding from the USDA, the researchers proposed to test nisin against Listeria monocytogenes, a deadly bacteria that poses a threat of food poisoning because it survives refrigeration. A 1998 outbreak of listeria poisoning in hot dogs killed 15 people and caused the recall of 15 million pounds of hot dogs and lunchmeats.
Cindy Bower, an assistant professor of bioresource engineering, carried out the research as part of her graduate studies leading to a Ph.D. in food science and technology. She investigated different ways to prepare and apply nisin to various surfaces. Her work showed that nisin adsorbed (formed a condensed layer) to surfaces and killed listeria bacteria that tried to attach to it.
"A lot of research is being done on nisin," Bower said. "Our research was unique in using nisin 'adsorbed to surfaces' rather than floating in a solution."
Nisin has a consumer-friendly advantage as a germ fighter. "It's a natural substance rather than synthetic and, unlike bleach, it's not toxic to humans. You can use it to clean countertops and, unlike other natural substances such as vinegar and lemon juice, it has no odor," Daeschel said.
Nisin is also easy and inexpensive to apply. "You can simply dip a material in nisin for a matter of seconds or minutes to create a protective coating," McGuire said.
In 1995, Daeschel and McGuire received a patent on the use of adsorbed nisin to prevent contamination, which led to interest in medical uses of nisin. Possibilities included surgery room clothing, surgical devices, soaps, sponges, mouthwash and toothpaste.
One of the most promising uses involved endotracheal tubes commonly used in hospital intensive care units. These tubes, which keep the air pathway to the lungs open, often become contaminated by strep or staph germs. "It has been estimated that 50 percent of the patients outfitted with endotracheal tubes get pneumonia. They either die or take longer to recover, so the problem is extremely serious," McGuire said.
Back in the lab, Bower set to work coating endotracheal tubes with nisin and testing their effectiveness against staph and strep bacteria. The research was successful. It is now being tested in cooperation with the OSU School of Veterinary Medicine.
More recently, the researchers have been working with Umpqua Research Company in Myrtle Creek, Ore., which has a National Aeronautics and Space Administration grant to study the effectiveness of surface-adsorbed nisin in spacecraft. "During long space missions, they're worried about the buildup of microbes on surfaces inside the spacecraft that could be a source of disease for the astronauts," Daeschel said.
The researchers are also looking at other beneficial applications of nisin. Daeschel is investigating the ability of nisin to inhibit spoilage bacteria in wine and beer (see sidebar).
Nisin also shows potential as an emulsifying agent to stabilize foods and medicines. In an emulsion, droplets of one liquid are dispersed throughout another liquid. In oil-and-water emulsions, the two liquids tend to separate into layers unless a third component, called an emulsifying agent, is present to keep the droplets dispersed.
Many food products are emulsions, including many dairy products, baked foods, ice cream products and mayonnaise. Properties related to dispersion are usually crucial in determining the acceptability of many products.
"Food products that employ nisin as an emulsifier would have the added advantage of being able to resist bacterial contamination," Bower said.
Nisin's emulsifying properties may also be useful in the search for drugs to combat cancer. Many chemical entities that hold promise for treating cancer never make it to trials because they resist being mixed into a solution. "They are difficult to solubilize (to make capable of dissolving easily in water). If they can remain dispersed, they are distributed better throughout the body where they eventually reach the cells that need the therapy," McGuire said.
Another trait of nisin-its ability to interact with human cells without causing harm-makes it a candidate for treating diabetes, a chronic disease caused by the body's inability to provide insulin. Without regular injections of insulin, a hormone that controls blood sugar levels, people with diabetes fall into a coma and die.
McGuire and Bower think nisin may enable diabetics to discard their hypodermic needles and administer insulin through a nasal spray instead. Insulin is most effective when administered directly into the bloodstream, bypassing the stomach and liver where some of it would be rendered inactive.
The nasal cavity has a large surface area, is easily accessible and has many blood vessels, making it a convenient site for administering drugs that must go directly into the blood, according to Bower. The problem lies in the nearly impenetrable upper layer of tissue in the nasal cavity that prevents materials from being transported through it in much the same way that skin forms a protective layer over the body.
McGuire and Bower think that nisin may promote the ability of insulin to move through the nasal membrane by opening the spaces between the membrane cells, allowing the larger insulin molecules to pass through.
The researchers originally planned to use laboratory rats, but decided to culture human tissue cells instead. "It made more sense to test with human nasal cells rather than try to extrapolate back to humans from an animal model," Bower said.
She obtains human nasal tissue from the Oregon Health Sciences University, where sinus surgeries are conducted on a regular basis. The tissue is a byproduct of the surgeries and otherwise would be discarded.
Unfortunately, for a substance that holds such promise, nisin is difficult to obtain. Its scarcity stems from the huge financial stakes surrounding much scientific research. At first the OSU researchers purchased nisin from a British company that used a proprietary method to produce it in quantity. But as the potential uses of nisin became apparent, the company required researchers to share any patents they developed from using its product. In response, the OSU researchers hope to launch a project to produce nisin in quantity.
Given the promising research results so far, it's likely nisin will be needed in large amounts in the future. It's an amazing substance that could greatly improve the quality of our daily lives through better food safety, medicines and medical procedures.
|NISIN FIGHTS SPOILAGE BACTERIA IN WINE, BEER|
While much of the OSU research on nisin has focused on food processing and medicine, this amazing bacteriocin was first used as a preservative to keep cheese and other milk products fresh. Food microbiologist Mark Daeschel, who holds the Nor'Wester Chair in Fermentation Science at OSU, has also investigated the use of bacteriocins as a preservative in wine and beer.
His research found that both nisin and lysozyme, an enzyme found in egg whites, inhibit spoilage bacteria in wine and beer.
"Lysozyme is being used as a preservative by the wine industry today. It breaks down the cell walls of bacteria, chews them up and digests them," Daeschel said.
His research may lead to the reduction or elimination of sulfite as a preservative in wine. That may be good news to people who cannot drink wine because they are allergic to sulfite.
A patent is pending for the use of lysozyme in beer and a petition is before the U.S. Food and Drug Administration to confirm lysozyme as a GRAS (generally recognized as safe) substance.