Biotechnology On The Food Safety Front

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By Matt Barron

With more than 11 million cases of food-borne illness in Canada every year, it may come as a surprise to some that several bacterial culprits of these ailments, such as salmonella, were not recognized as causes of food-borne illness until 25 years ago.

These pathogens are certainly not new: escherichia coli (E. coli), listeria, salmonella and other bacteria have long existed in the environment, and several have evolved to live in the gut of animals. While many cases of foodborne illness can be traced to poor food handling practices, and most immune systems can handle the pathogens, the organisms can cause hospitalization and even death.

Staying one step ahead of these emerging diseases is a major challenge for researchers. It’s a challenge that spans the whole spectrum of food production, from the farm to the processing plant—as illustrated by the tainted deli meat at an Ontario meat-packing plant, which left 12 Canadians dead last year.

“Food-related illnesses are becoming more common,” says Andrew Potter, director of the University of Saskatchewan’s Vaccine and Infectious Disease Organization, “and as antibiotic resistance grows, we need to be looking at new defenses.”

Vaccinating for safer food
Researchers at VIDO, a world leader in the research and development of vaccines for humans and animals, are tackling the problem from the agricultural end of the spectrum: the farm, where bacterial pathogens thrive.

The researchers’ goal is to prevent colonization of livestock in their intestinal tracts by such microorganisms as E.coli O157:H7, the cause of the 2000 outbreak in Walkerton, ON. They are also working on minimizing in livestock and poultry the presence of Campylobacter jejuni, which causes severe diarrhea and can lead to chronic complications such as Guillain-Barre syndrome—and the now infamous Listeria monocytogenes.

Vaccination is the new defense being developed by Potter and fellow VIDO scientist Wolfgang Koester, both of whom hold NSERC (National Sciences and Research Council of Canada) industrial research chairs in food safety. This vaccine, however, differs from the typical one given for the flu or mumps.

Rather than initiating an immune response to simply fight off invading organisms in a non-specific fashion, the vaccine boosts immunity to drastically reduce the natural colonization of a bacterium.

“If we could reach the goal to reduce pathogen numbers in livestock,” says Koester, “down-stream processing from slaughter houses to the production line would be less risky, and you could come up with safer food.”

More than 10 years ago, Potter and his University of British Columbia colleague, Brett Finlay, developed a vaccine to control E. coli O157:H7 in cattle—in order to minimize its transmission to humans.

The vaccine exploits the mechanism by which the bacterium colonizes the animal gut, a process that could rival the imaginings of a science fiction writer.

Armed with a tool resembling a syringe, the bacterium finds a host cell in the intestine and sits on it. The bacterium then injects specific proteins into it, allowing the organism to cling to the cell. In this manner the bacterium colonizes the gut.

The vaccine works by helping the animal build up antibodies against the proteins, disarming the bacteria. Potter has been expanding this concept to vaccination against Campylobacter and Salmonella, the top two bacterial causes of foodborne illness.

The salmonella vaccine, developed with Koester, would deal with a common problem: Salmonella contamination from poultry and eggs. Since the bacterium can enter the embryo before the egg is formed, a vaccine might prevent the bacterium from being transmitted from the hen’s gut to her ovaries, where it could infect the embryo and potentially transmit salmonella to the person eating the egg.

“If we could prevent this from happening,” says Koester, “you could potentially one day have a safer egg, and the broiler chicks could be hatched salmonella-free.”
Many of the diseases being studied for vaccine development are largely classified as Level 3 Containment, but there is a worldwide shortage of facilities in which to study CL3 diseases or test new vaccines against these diseases.

The researchers will be using the InterVac facility, set to launch in 2010 at the University of Saskatchewan. Expected to be largest Level 3 laboratory in the country, and to advance food safety and vaccine research, Intervac will be used to conduct trials for, among many other vaccines and immune-boosting technology, a proposed listeriosis vaccine.

Listeria vaccination
There is currently no vaccine against listeriosis available today, so VIDO has added the bacterium to the list of animal vaccine targets under their $4-million food safety research program.

The listeria bacterium—like pathogenic E. coli (which causes so-called “hamburger disease”) and campylobacter—can be transmitted directly to humans via contaminated food or indirectly by environmental contamination.

Though healthy people exposed to listeria are rarely affected by the bacterium, it is more likely to result in death than other bacteria that cause food poisoning—particularly in such high-risk individuals as the elderly, children and pregnant women.

It is impossible to completely eliminate the pathogen, says Koester, as it’s found in soil, vegetation, water, sewage, silage and human feces. Reducing the prevalence of listeria in food-producing animals, however, could significantly improve the overall safety of our food production, processing and distribution, even water.
Potter warns that vaccination for these diseases is “not a magic bullet.” Vaccination should be used in conjunction with other management methods on the farm, such as reducing the manure which can become a hotbed for pathogens.

As with E. coli, Potter anticipates that it will take the combined efforts of many different partners—industry, government, agricultural producers and a large team of scientists, postdoctoral fellows, graduate students and technicians—to reduce the listeriosis threat.

Tenacious bacteria
A major front for the prevention of food borne illness lies at the other end of the spectrum: the food processing facility itself.

Research at the University of Saskatchewan, one of two prominent universities studying food safety and quality in Canada, along with Guelph University, has been focusing on the pathogenic bacteria, which cling to the surfaces of food-processing machinery, called biofilms. A biofilm is believed to be the source of the listeria-contaminated Maple Leaf products.

“Biofilms are found in many places—on a rock or in a river, even on your teeth.” says Darren Korber, an associate professor in the Food and Applied Microbiology department. “And they are the enemy in many of these foodborne illness cases.”
Bacteria partial to biofilms—listeria, salmonella and campylobacter—exhibit an adaptive genius which makes killing them extremely difficult. By residing in biofilm formations, which consist of live and dead bacteria and polymers, the organisms become about 1,000 times more resistant to antimicrobial agents than if they had to survive by themselves.

Since 1994, Korber has been investigating the ecology of biofilms and testing ways to control them. The microbiologist has found the films to be very complex, almost an organism in itself with tunnels and execretory pores—not unlike a very basic circulatory system in an animal.

Korber has been testing chlorines and other antimicrobial agents to control the bacterial agents. The problem is that listeria and other bacteria take refuge deep within the film, in little pockets, thereby putting them beyond reach of the most pungent cleaners.

If a cleaner misses a bacterium the first time, he says, that bacteria will be twice as resistant to the cleaner the second time.

Most industrial plants, Korber says, conduct scheduled cleaning and maintenance after every shift. The reason for this is that sometimes the deeply embedded bacteria survive the cleaning, and immediately start growing before the next cleaning. “You have to keep knocking them back as best you can, but you can’t get them all,” he says.

Dismantling Factory Machines
It wasn’t so much that Maple Leaf company “failed to do the kind of quality control it was supposed to be doing, or as effectively as it could,” says Korber. The problem had to do with the machines themselves.

“You can’t dismantle all of your equipment, after every shift, and take the bearings and go right to the very basics of machine every time,” Korber says. “The machines were never designed to be cleaned. They have new protocols where they are dismantling the equipment after every shift.”

The types of improvements that could be made to food processing systems, Korber says, have more to do with the plant equipment itself than with its operation. “This is the only way you’re going to get these last microorganisms.”

There also may be potential for biotechnology—besides the E. coli or salmonella vaccine and other advances—to battle the organisms at the level of biology.

By providing a better understanding of these bacteria—and possibly finding the molecule or gene on which the bacteria rely for creating their biofilms, and thus providing resistance—Korber hopes to find a weak point in their defenses. One possibility is a strategy targeting a gene involved in creating a mature biofilm.
Even then, Korber says, it is impossible to ensure food products are 100% safe.

Only irradiation of the packaged food could kill all of the organisms, a technique that doesn’t sit well with the public—who would still be responsible for avoiding cross-contamination once the food is removed from its packaging.

“You can never kill all of these bacteria, and so it’s a matter of time before something happens. It’s just a feature of the industry and the world we live in.”

Matt Barron is a writer with the University of Saskatchewan Research Communications.