Bioterrorism and Your Food
"Tragically, terrorists are very inventive," says Claire Pomeroy, chief of infectious diseases at UK, as she talks about an unsuccessful, but eye-opening, domestic bioterrorism attack.
In September 1984, a 10,000-member cult led by Bhagwam Shree Rajneesh used Salmonella to contaminate salad dressing and coffee creamers at 10 restaurants in the Oregon town of The Dalles. Their goal: change the outcome of the November election for county commissioner by food-poisoning voters. At least 751 people became sick. "They didn't succeed in affecting the election, but this attack made it clear that this kind of thing is within the realm of possibility. These cult members had no special training," Pomeroy adds.
"With bioterrorism, they don't really need to succeedall they need to do is put doubt in people's minds," says Melissa Newman, a microbiologist specializing in food safety and animal nutrition in the UK College of Agriculture.
Salmonella, the number one food-borne pathogen, tops UK scientists' list of most-studied bacteria, a list that also includes E. coli, Shigella, Listeria, and Staphylococcus aureus.
"Not all bacteria on food are harmful," says Newman, who came to UK five years ago from a microbiology company in Cincinnati. "You have a natural population of bacteria that sit on the surface of fruits and vegetables and that are benign."
Food-borne pathogens can taint fruits and veggies at a variety of stages in production. It can happen in the field (spread by animals or contaminated irrigation lines), and it can happen at harvest (with poor-quality rinse water). It can happen in transport (refrigerated trucks or railcars that are dirty or contaminated by the last thing they hauled). And it can happen in your kitchen.
"Most food-borne illness occurs at home as a result of cross-contamination. Mom cuts up the chicken and the tomatoes on the same cutting board," Newman says. Besides eliminating cross-contamination, the best way to protect your family is by refrigerating and then thoroughly washing fruits and vegetables.
Fighting pathogens in the field: (left to right) Thomas Kemp (horticulture professor), Katherine Akers (research analyst), Melissa Newman (animal sciences assistant professor), and Randy Collins (research analyst)
"Most people think products like Fit [a shampoo for fruits and veggies] were put on the market to get rid of bacteria. But most of those products are designed to rinse off pesticides," Newman says. "The washing process itself takes care of most of the bacteria."
While not common, there have been several food-borne bacterial outbreaks. "Awhile back we had problems with E. coli 0157:H7 in unpasteurized apple juice and cider," Newman says. The problem with this bug is its acid tolerancethe natural acids in apples don't inhibit the bacteria's growth. "This E. coli is naturally found in cows, but it's not harmful to them because they don't have the same intestinal structure as humans," she says. "It's a fascinating organism because it's the poster-child of bacterial survival. The sad part is it targets infants and young children with inexperienced immune systems." E. coli 0157:H7 can cause irreversible damage to the kidneys resulting in death.
After the E. coli 0157:H7 outbreak, orchards made new rules. One, no picking apples off the ground. "If they're on the ground, they're bruised and the pathogen can get inside," Newman says. Two, no fertilizing with fresh manure. "In some cases orchards were running cows through, so the manure was really fresh," she says. "The cows would eat the apples on the ground and then deposit their own apples."
E. coli has also caused problems in sprouts. Contaminated radish sprouts caused an outbreak in Japanese school children, and alfalfa sprouts, grown in the United States, have been plagued by the bug. Newman is using natural compounds from strawberries"components of the strawberry odor and flavor"to fumigate sprout seeds to prevent bacteria from growing.
Before Newman came to UK, Thomas Kemp and Doug Archbold, in the horticulture department, had been looking at the ability of these natural compounds to deter mold growth on strawberries. "I wondered what would happen to pathogens on sprout seeds treated with the compounds," she says. It turns out this approach has been pretty effective at killing Salmonella and E. coli, and the treatment doesn't affect the speed of germination. Newman is also looking at fumigating the sprouts themselves.
Kemp says these compounds, known as natural plant volatiles, are vapors given off by most plants. "These compounds are the aroma you detect when you eat them," he says. Kemp, Archbold and Newman are partners on a project to detect pathogenic vapors by "sniffing" the air around produce with a special device called a solid-phase microextractor (below).
"It's a syringe with a hollow, half-inch-long glass tube inside the needle. The tube walls are coated with liquid that will soak up any vapors in the air," Kemp explains. "We then flash-heat the vapors off (at about 200 degrees Celsius) into an instrument called a gas chromatograph that separates out all the components." This technology, developed in the early '90s, was created by the EPA to look for pollutants in the air. "It works quite well for this too," Kemp says.
The beauty of this process is that it's nondestructivethe air around the fruit is sampled, not the fruit itself.
Kemp's hope was to find markersdistinct sets of chemicalsgiven off by pathogens growing on fruits, veggies or meats. "We found that the markers for the vapors bacteria make are very different from what plants make. Bacteria make a special type of alcohol that our instrument can detect.
"Melissa and I have talked about a handheld device, sort of like a breathalyzer, for consumer use that could detect what's in the air around produce. It's not unrealistic to think you might have something like that in your kitchen in the future.
"Our food supply sources have changed," Kemp says. "More and more produce is coming from other countries, and what is grown here is produced on huge farms."
Newman says these large food-processing companies are well aware of bacterial, as well as bioterrorism, risks.
"I think the threat of bioterrorism is more attractive to would-be terrorists than actually going through with an attack," she says. "Most of these bacterial agents won't give them the end producthigh fatalitiesthey want; they'll just incapacitate people for a short time."
She cites Staphylococcus aureus as an example. "Most of us carry it on our skin, but under the right conditions it can produce a heat-stable toxin. If this toxin were in your food, it would make you sick to your stomach for four to six hours."
Antibiotic Resistance: The Real Threat
Newman's main passion is antibiotic resistance. "We get caught up in talking about antibiotic-resistant bacteria. It's not bacteria in and of themselves that's really the issueit's the genetic material they transport." She explains that bacteria share genetic materialthey copy plasmids (extra pieces of DNA) and hand out copies to their neighbors. These copies can include resistance to one or many antibiotics, and bacteria aren't xenophobic about sharing this information. "Genetic material can be transferred from this E. coli to that E. coli to a Salmonella," she says. "This material can come from nature, and it can come from human use."
Newman says while antibiotic resistance is natural (microorganisms naturally arm themselves with antibiotics to compete for nutrients), humans are exacerbating the resistance. "Doctors who prescribe antibiotics to treat the flu contribute to it, since the flu is caused by a virus, not bacteria. Individuals who use antimicrobial hand washes contribute to itthe mode of action of those hand washes is very similar to the action of many antibiotics.
"You sometimes hear people say the problem with our health today is that we don't eat enough dirt as a child. In some ways that's true." She says the widespread use of antibacterial cleaners and washes is basically promoting a bacterial population that can survive these chemicals.
Newman says the farm also plays a role in antibiotic resistance. Antibiotics are used on the farm primarily to prevent illness in healthy livestock and to speed up growth to increase production. "We need to focus on conservative use of antibiotics," she says. Europe has banned the use of almost all antibiotics in animals. In the United States, the Alliance for Prudent Use of Antibiotics recently recommended we stop using antibiotics for increased production, but allowed use to treat illness.
"The number of people who die from antibiotic-resistant bacteria is unclear," Newman says. "There has been some sensationalization, but we need to act now to get out in front of this. There are natural alternatives to antibiotics, and certainly big companies realize this." Tyson's has reduced or eliminated antibiotic use in its poultry, a fact the company touts in its advertising. "For a long time people have said, 'If we stop using antibiotics, resistance will go away.'"
But Newman says that's not true, as evidenced by the herd of pigs the College of Agriculture has in Princeton, Kentucky. "These animals have not received any antibiotics for almost 30 years, and still significant amounts of antibiotic resistance can be detected. This research has provided a great deal of evidence that things like heavy metals in the environment, fertilizers and sanitizers encourage bacteria to hang onto antibiotic resistance."
She says, "Resistance is something we have to address because antibiotics are the key to all modern medicine."
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