Posts Tagged: Bacteria
E. coli and Salmonella are rare in wild birds, Campylobacter more common
Concerns over foodborne risk from birds may not be as severe as once thought by produce farmers, according to research from the University of California, Davis, that found low instances of E. coli and Salmonella prevalence.
While the research found that the risk is often low, it varies depending on species. Birds like starlings that flock in large numbers and forage on the ground near cattle are more likely to spread pathogenic bacteria to crops like lettuce, spinach and broccoli, according to a study of food safety risk and bird pathogens from the University of California Davis. In contrast, insect-eating species were less likely to carry pathogens.
The findings, published in the journal Ecological Applications, suggest that current practice of removing bird habitats around produce growers' farms over concerns the animals could bring foodborne pathogens into their fields may not solve the problem.
“Farmers are increasingly concerned that birds may be spreading foodborne diseases to their crops,” said Daniel Karp, the senior author on the study and an assistant professor in the UC Davis Department of Wildlife, Fish and Conservation Biology. “Yet not all bird species are equally risky.”
Only one foodborne disease outbreak in produce has been conclusively traced to birds: a Campylobacter outbreak in peas from Alaska. While the bacteria can cause diarrhea and other foodborne illness in humans, it's less of a concern to growers than E. coli and Salmonella, which have been responsible for multiple outbreaks across the nation.
In this study, researchers compiled more than 11,000 bacteria tests of wild bird feces and found that Campylobacter was detected in 8 percent of samples. But pathogenic E. Coli and Salmonella were only found in very rare cases (less than 0.5%).
In addition to the bacteria tests, researchers conducted roughly 1,500 bird surveys across 350 fresh produce fields in Western states and collected more than 1,200 fecal samples from fields. They then modeled the prevalence of pathogens in feces, interactions with crops, and the likelihood of different bird species to defecate on crops to determine risk.
Insect-eating birds pose lower risk
Based on the data, insect-eating birds, such as swallows, present a lower risk, while birds that flock near livestock, such as blackbirds and starlings, are more likely to transmit pathogens.
The data can help the agricultural industry determine risk and take action, such as separating produce crops from cattle lands. They also don't need to treat all birds the same.
“Maybe farmers don't need to be quite as concerned about all types of birds,” Karp said. “Our data suggest that some of the pest-eating birds that can really benefit crop production may not be so risky from a food-safety perspective.”
Removing habitat can backfire
This study and the authors' prior work indicate that removing habitat around farms may actually benefit the species that pose more risk and harm the beneficial, pest-eating ones that are less risky to food safety. This is because many prolific insect-eaters may visit crop fields to eat pests but need nearby natural habitats to survive. In contrast, many of the bird species that most commonly carry foodborne pathogens readily thrive on both cattle farms and produce farms without natural habitat nearby.
Insect-eating birds that forage in the tree canopy pose minimal threat because they are less likely to carry foodborne pathogens and come into direct contact with produce. They can also be valuable parts of the ecosystem, particularly if they eat pests that can harm crops. Installing bird boxes could attract the pest-eaters, as well as help with conservation efforts.
“We basically didn't know which birds were problematic,” said lead author Olivia Smith, a postdoctoral researcher at Michigan State University who was at University of Georgia when the paper was written. “I think this is a good step forward for the field.”
Additional co-authoring institutions include James Cook University, UC Berkeley, UC Riverside, University of Kentucky, University of Texas, Virginia Polytechnic Institute and State University, Washington State University, BioEpAr, The Nature Conservancy and Van Andel Institute.
The research was funded by the United States Department of Agriculture and the National Science Foundation./h3>/h3>/h3>/h2>
Discolored leaves. Decaying roots. Dead wood. Mother Nature offers a fascinating and colorful backdrop of clues to track microscopic killers. Much like any medical mystery, experts are called in to diagnose or identify a disease from its symptoms and recommend management strategies to prevent further damage or loss of healthy plants.
Humans and animals depend on plants for their food supply and ultimately for their survival. When diseases threaten crops, a high-quality, affordable food supply is placed at risk. For growers, plant diseases can reduce crop yields. For consumers, reduced crop yields can drive higher food prices. Plant pathology research holds enormous implications for a sustainable food supply.
Florent Trouillas, who was named UC Cooperative Extension specialist in the Department of Plant Pathology at UC Davis and the Kearney Agricultural Research and Extension Center last year, explains the bottom line of most concern to growers.
"Once we identify a disease causal agent, a main question remains from growers. What growers really want to know is how to control the disease and prevent its spread to new healthy plants; they look to the University of California for solutions," Trouillas said.
A crisis in the food production system can impact other areas of society as well. In fact, history is filled with examples of how plant diseases influenced economies, environments and human societies.
Another historical illustration of plant pathology research occurred in the 1920s. The most common trees in the forests of the United States at the turn of the century were the majestic American chestnuts. The trees generated income for humans and the timber industry, served as a food source for people and animals, and provided habitat for wildlife. Then the trees started dying, until by the late 1920s, they had become the first tree in modern times on the brink of extinction. Plant pathologists were particularly adept at identifying plant diseases by this time and diagnosed the Cryphonectria parasitica fungus as the cause of the chestnut blight. By preventing the extinction of the pivotal species, plant pathology had a direct impact on the economy and the environment.
More recent major plant disease outbreaks in the United States involving plant pathology research have included Sudden Oak Death with devastating effects in California and Oregon forests, pitch canker killing California native pine species, and citrus canker in Florida, which has had a huge economic impact on the industry.
Veterinarians treat diseases in animals, physicians in humans. Trouillas describes the role of plant pathologists in similar terms. “We study the pathology of plant systems. Plant pathologists treat plants," he said.
Healthy plants ensure a sustainable food source and habitat for so many other organisms, including the human species.
Michele Jay-Russell, a veterinarian and research microbiologist at the Western Institute for Food Safety and Security (WIFSS) and program manager of the Western Center for Food Safety (WCFS), recently co-authored a study that highlights the need to be aware of the hazards associated with using raw animal manure to fertilize home gardens. (Read full article here.)
The basis for the study began in July of 2010 when a shire mare from a rural Northern California farm was brought to the William R. Pritchard Veterinary Medical Teaching Hospital for treatment of colic. Following protocol, the veterinarians on call screened the horse for Salmonella to avoid infecting other horses during hospitalization. She tested positive and after successful treatment for colic, went home. Her owners then notified the veterinarians that some of their other draft horses were sick as well — all 8 were tested and 6 came back positive for the same Salmonella Oranienburg strain, including the mare that still had the infection.
Jay-Russell heard about the case from her colleague John Madigan, professor of medicine and epidemiology at the school. The farm’s owners invited Jay-Russell and Madigan to the farm to see if they could uncover the source of the Salmonella infection. They sampled water from horse troughs, manure storage piles, wild turkey feces and soil from the family’s edible home garden where raw horse manure had been used as fertilizer. Each of those locations had a percentage of positive samples over the sampling period from August 2010 to March 2011.
“We showed the owners how to continue collecting samples and provided them with a FedEx number to ship them to UC Davis,” Jay-Russell said. “During that whole time, the garden soil kept coming back positive, which showed that this strain of Salmonella could persist for months.”
While the researchers couldn’t be completely certain about the original source of Salmonella on the farm, they suspect that a recent surge in the wild turkey population on the property introduced the bacteria to the horses by pooping in the horse corrals and in the water troughs. They speculated that the wild turkeys brought the Salmonella onto the property, although they couldn’t rule out the possibility that the birds were exposed on the farm or to other potential sources of Salmonella.
“What is clearer is that the raw horse manure applied as fertilizer was the most likely source of garden soil contamination,” Jay-Russell explained. “We suspect that the damp climate in Mendocino County may have contributed to the longevity of this bacterium in the soil long after the owners stopped applying the horse manure to the garden. Fortunately, the owners didn’t get sick, but our investigation showed the potential for widespread dissemination of Salmonella in a farm environment following equine infection.”
To promote safe gardening practices, Jay-Russell has teamed with Trevor Suslow, a Cooperative Extension food safety specialist in the Department of Plant Sciences, to speak to groups of small farmers around the state about best practices. They also use a brochure in English and Spanish, “Food Safety Tips for Your Edible Home Garden,” that includes information about safe uses of animal manure and ways to minimize animal fecal contamination.
“It’s good to let people know about the risks and to correct misinformation about ways to treat the compost pile before using it in the garden,” Jay-Russell said. “The biggest take home message from this experience is to be very careful about using manure from sick horses — and to be cautious about offers of free manure — you don’t know what’s in there. Commercial compost should be bought from a reputable source.”
She urges gardeners to take a class and learn how to compost correctly and safely. Each county in California has UC Cooperative Extension advisors and many have Master Gardener programs offering information on food safety.
Bart Weimer, professor in the UC Davis School of Veterinary Medicine, serves as director of the 100K Genome Project and co-director of the recently established BGI@UC Davis facility, where the sequencing will be done. Other collaborators include the U.S. Centers for Disease Control and Prevention and the U.S. Department of Agriculture.
The new five-year microbial pathogen project focuses on making the food supply safer for consumers. The group will build a free, public database including sequence information for each pathogen's genome — the complete collection of its hereditary information. The database will contain the genomes of important foodborne pathogens including Salmonella, Listeria, and E. coli, as well as the most common foodborne and waterborne viruses that sicken people and animals.
The project will provide a roadmap for developing tests to identify pathogens and help trace their origins more quickly. The new genome database also will enable scientists to make discoveries that can be used to develop new methods for controlling disease-causing bacteria in the food chain.
"This landmark project will revolutionize our basic understanding of these disease-causing microorganisms," said Harris Lewin, vice chancellor for research at UC Davis.
The sequencing project is critically important for tackling the continuing outbreaks of often-deadly foodborne diseases around the world. In the United States alone, foodborne diseases annually sicken 48 million people and kill 3,000, according to the CDC.
"The lack of information about food-related bacterial genomes is hindering the research community's ability to improve the safety and security of the world food supply," Weimer said. "The data provided by the 100K Genome Project will make diagnostic tests quicker, more reliable, more accurate and more cost-effective."
"We see this project as a way to improve quality of life for a great many people, while minimizing a major business risk for food producers and distributors," said Mike McMullen, president of Agilent’s Chemical Analysis Group.
A consumer-focused article about the project is available on the FDA website.
(This article was condensed from a UC Davis news release. Read the full press release and watch a video of Bart Weimer giving an overview of the project.)
According to Dr. Trevlor Suslow, a plant pathologist and Cooperative Extension specialist at UC Davis, “Americans consume more than six billion servings of uncooked fresh fruits and vegetables every year, versus a very small number of illnesses that are clearly linked to foodborne pathogens.”
The take-home message is that the food supply in the U.S. is generally very safe, particularly when everyone in the food supply chain (including consumers) does their part to assure food safety.
The U.S. Food and Drug Administration (FDA) recently released the following information for home consumers:
Nearly 48 million people (1 in 6 people) are sickened by food contaminated with harmful germs each year, and some of the causes might surprise you.
Although most people know animal products must be handled carefully to prevent illness, many don’t realize that produce can also be the culprit in foodborne illness. In recent years, the U.S. has had several outbreaks of illness caused by contaminated fruits and vegetables — including spinach, tomatoes, and lettuce.
Fresh produce can become contaminated in many ways. During the growing phase, fruits and veggies may be contaminated by animals, harmful substances in the soil or water, and poor worker hygiene. After produce is harvested, it passes through many hands, increasing the contamination risk. Contamination can even occur after the produce has been purchased, during food preparation, or through inadequate storage.
The FDA says to choose produce that isn’t bruised or damaged, and make sure that pre-cut items — such as bags of lettuce or watermelon slices — are either refrigerated or on ice both in the store and at home. In addition, follow these recommendations:
- Wash your hands for 20 seconds with water and soap before and after preparing fresh produce.
- Cut away any damaged or bruised areas before preparing or eating.
- Gently rub produce while holding under plain running water. There’s no need to use soap or a produce wash.
- Wash produce BEFORE you peel it, so dirt and bacteria aren’t transferred from the knife onto the fruit or vegetable.
- Use a clean vegetable brush to scrub firm produce, such as melons and cucumbers.
- Dry produce with a clean cloth or paper towel to further reduce bacteria that may be present.
- Throw away the outermost leaves of a head of lettuce or cabbage.
Store perishable produce in the refrigerator at 40 degrees or below.
(Condensed from an FDA news release. The site has an interesting video and useful links to other sites with food safety information.)
For more on what UC Davis and UC Cooperative Extension are doing to assure the safety of fresh produce:
- UC Food Safety website
- Postharvest Technology Center website
- Center for Produce Safety website
- UC publications